You may be able to find one online or at a local paralegal service. You are going to need to explain why you did not respond within the time allowed, such as you were not served or did not otherwise get notice of the hearing, or were given notice too close in time for the hearing to appear or obtain counsel to appear for you.
As to the Motion to Set Aside the arrearage that has been assigned, if the default is set aside, the arrearage resulting from not appearing at the hearing should be set aside as well. Obviously, the other side is not going to be happy about this result, and is likely to oppose the motions. If there is any way to have back up support as to the grounds for the motion (someone else who was served in your stead forgot to give you the summons and will give an Affidavit to that effect, someone else lives at your old address where the summons was supposedly sent and will swear they never saw it, etc.) that will be a big point in your favor.
Granting the motions is discretionary with the court, but most judges will agree to set the default aside so that the matter may be determined on its merits. This is particularly true in family law, as you can come in with a Motion to Modify the court's earlier Order(s) if the Motion to Set Aside the default is not granted.
If at all possible, I suggest that you obtain a local family law attorney to represent you in this matter, as the attorney will know how to best present the matter to the judge to achieve the best result.
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