Hi, I'm Nathan.
Sorry to hear that you're having trouble with this but I'll do my best to help you.
Unfortunately, no, this is not an option.
Your current system is a very old and obsolete model, having been replaced 8+ years ago by the DECT 6.0 format.
There are no parts for your system and no range extenders were offered at the time.
At this point, your best option would be to replace the system entirely.
You may very well find that the newer systems, which are all digital, have sufficient range on their own, but a range extender is available as well.
I'd be happy to recommend a system for you, but do you actually need 2 phone lines? Or is a single line sufficient?
How many cordless handsets do you need?