I have them new from the engine rebuild kits I have brought in over the years and sell for $3 as seen below and can ship from NC to CA 1st class letter rate (no tracking) for $2, or 1st class parcel for $4 (tracking), or 2-3 day priority (tracking) for $8 for a total of $5, $7 or $13 depending on shipping preference. Shoot me a PayPal to firstname.lastname@example.org and will have one on the way tomorrow morning. If you don't have PayPal email me at email@example.com and I can send an invoice so you can pay with credit/debit card.
It is just a round cork gasket. You can easily make one by getting a sheet of cork material from any auto parts store. be sure to use a new razor blade.
Russ is right. These are easy to make using a sheet of cork rubber gasket, a utility knife, and a steady hand. The issues is sometimes getting a good template. If you have an old gasket available the easiest method is to lay on a piece of paper and spray with rattle can paint, lift the old gasket and there is your template. Simply overlay on the gasket material and use a utility knife to cut out. Since this is just a circle, so you can measure the inner and outer diameters and draw the circle on a piece of paper, overlay the gasket and cut out.
Since I have the new gasket in my hand here are the specs: ID 1 3/8", OD 1 7/8", 1/8" thick, 1/4" width.
For small gasket projects, I like the Fel-Pro 3060 4 pack gasket set. It's $9.39 via Amazon and if you are a Prime Member (who isn't!), it will be delivered to your door free in 2 days. I just re-upped last week. Our local AutoZone sell for $8.99 but the 40 cents savings is not worth it and I can wait 2 days! For the Amazon link Click Here. They also sell individual sheets of different gasket material. For the 4 pack set here is what is included:
One cork-rubber sheet = 10"x 8 5/8" x 1/8"
One cork-rubber sheet = 9 1/8" x 8 5/8" x 1/16"
One rubber-cellulose sheet = 9 3/4" x 8 5/8" x 3/64"
One rubber-fiber sheet = 9 1/4" x 8 5/8" x 1/32"