Hi Cynthia, I’ve bought gaskets at MEC a few times. I just checked, and they still have them on their website https://www.mec.ca/en/product/1906-320/Latex-Neck-Gasket?org_text=gasket. You can call to see if they have any in stock.
I’ve replaced the gaskets on my dry suit a few times. As long as you have some Aqua-Seal glue and don’t mind making a mess, I found the process not too difficult. I used a large balloon to keep the neck open when I replaced that gasket. I might’ve used a lightbulb or something similar in the wrist and ankle gaskets. If you want any other info or help with it, give me a call – 604-434-2294