I used to work with your model panel back with it was new, in the 90's.
I wish you luck in finding those items. Napco is a good brand, but they got started using RF (wireless) late in the game, and those models were in production (IINM) for only a few years before Napco discontinued them when they upgraded their product line to the GEMINI series. The new GEM RF receivers and sensor/transmitters were incompatible with the R1000/T1000 series.
In other words, there weren't that many out there when they stopped making them about 20 years ago. I'm guessing the chances of finding any are slim, more so if you're trying to find more than a few, BUT...I haven't worked with old Napco panels in over 10 years, and somebody who does work with them might be able to help.
I recommending repeating your post on this forum:
https://www.doityourself.com/forum/electronic-home-security-systems-alarms-devices-87/
which is specifically for DIY security systems, and has alarm security techs frequent it. Someone may have some old RF Napco parts stashed on a shelf somewhere.
Sorry, I can't be more help, but all my older RF salvage stuff is other brands.