Found all three PDQ. Google can be your friend.
Although I found those gaskets, they seem pretty pricey. You may want to consider making your own, it's really not all that hard. Most auto parts stores sell 1/16" gasket material in rolls up to 18" X 36". It can be bought in larger sheets other places.
If you can get the cover out of the way to be able to work all that's really needed is proper sized gasket material, a couple medium sized ball pein hammers, the sharper point on the end the better, and most importantly a working steam iron to flatten out the rolled material, and a makeshift ironing board out of plywood, etc. And some patience. I made nearly all of the gaskets on my Farmall 130 & 140 when rebuilding the rearends & PTO's.
You'll want the surface cleaned up. For smaller area gaskets, cut a piece slightly larger that needed. Lay it on the piece you're making the gasket for. Take the pointed end of the hammer and tap out the bolt holes first. I have multiple ball pein hammers in the 6 oz. to 12 oz. range specifically for this purpose. Get eh bolt holes tapped out one at a time, then insert a bolt to hold the sheet in place. Once all bolts are in place, start tapping on the inside edge. Most castings are sharp enough hitting right on the very edge with the pointed end will easily cut the gasket material. Depending on how large of a piece you're working on like the transmission case, once you've made the initial pass seeing the edge of the case working 3" - 4" at a time, you can turn the hammer over and use the flat end to cut it more cleanly.
You will more than likely end up with a few fuzzies on the edges. For this, take a good sharp utility knife, and rake backwards on those edges, and it will take those off.
I use Permatex brush on gasket sealant. Usually High Tack, or Aviation sealer. Both seal well but if needed can be taken back apart without tearing the gasket. Re-seal and put back on.
You'll no doubt have a large piece from the center of the transmission case left over. I save those pieces in a larger box for another job, another day. I know between those 2 tractors I saved well over $200 making my own gaskets. That money saved went towards bearings & seals.
We had an old school mechanic at work that taught me that, and more than several other things. He made a lot of things, even specialized tools for certain jobs.