I'm sorry I did not get back to you last night. I went offline after my last response.
From the facts that you've described, including that defense counsel knew that the government would rely on an expert several months before the trial, and the hearing the day before the trial, and the trial itself, it may be that the defendant does not need either the affidavit of defense counsel or his testimony.
Here is a case - it is federal that deals with similar issues in the context of a murder case. http://ocdw.com/pdf/20060626/RedElk.pdf It is instructive because it discusses the issues that appear to be germane to your argument regarding the expert testimony. From this case the defendant can determine the points to concentrate on.
First, the defendant needs to state when the prosecution disclosed to defense counsel that it intended to rely on an expert and the extent of that disclosure so that it could be explored and met.
If the prosecution did not disclose sufficiently, then defense counsel should have followed-up on the disclosure, either informally or requesting the court to compel disclosure. Either way, for purposes of the Petition, the defendant can conclude that defense counsel knew he would need an expert or something to challenge the expert at the time of disclosure. The OK rules of criminal procedure can be found here http://www.oklegislature.gov/tsrs_os_oc.aspx Title 22 sec. 2001-2002 (starting on p. 448).
The rules include §22-2002. Disclosure of evidence - Continuing duty to disclose - Time of discovery - Regulation of discovery - Reasonable cost of copying, duplicating, and videotaping.
A. Disclosure of Evidence by the State.
1. Upon request of the defense, the state shall be required to disclose the following:
a. the names and addresses of witnesses which the state intends to call at trial, together with their relevant, written or recorded statement, if any, or if none, significant summaries of any oral statement,
b. law enforcement reports made in connection with the particular case,
c. any written or recorded statements and the substance of any oral statements made by the accused or made by a codefendant,
d. any reports or statements made by experts in connection with the particular case, including results of physical or mental examinations and of scientific tests, experiments, or comparisons, . . . .
Second, the defendant should include when the court required, if it did, that experts be disclosed. There should have been a preliminary hearing early on in the case where the court ordered a discovery schedule or that evidence be revealed by a certain date. If this date was not met, then that was an additional grounds for challenging the admission of the expert witness. I'm thinking defense counsel in the defendant's case did not request discovery sanctions such as that granted in the case above. Either this was because there was no discovery abuse or because he just didn't ask.
Third, defense counsel did not seek a continuance, did not request funds for an expert and did not retain and expert or have an expert at trial, although he had an opportunity to do so. This can be established from the record.
Fourth, you can note that the court in the case above also mentions Daubert and how meaningful it is to have the opportunity to challenge expert testimony on that basis. The record in the defendant's case will also reflect that defense counsel did not request a Daubert hearing.
Fifth, the trial transcript would show that defense counsel did not present an expert, and possibly that he did not challenge the state's expert meaningfully on cross-examination, although there were learned treatises available that could have been used to impeach the expert and his conclusions.
So, the only piece the defendant needs that might not be contained in the record is when defense counsel learned that the government would use an expert at trial.
In addition, the organization norml may be able to help you find scientific evidence you can use. I wouldn't use them as a primary source because they have a specific agenda and lobby. However, they may be a good resource for information you are looking for. Here is an article on the DUI drug laws and zero tolerance states. http://norml.org/library/item/you-are-going-directly-to-jail
Oklahoma is not a zero tolerance state with regard with regard to DUI drugs. See statute Title 47, sec. 11-902.
Please feel free to ask any follow-up questions.