There are on Ebay. There is no gasket inside the tube. it's on the crown.
BTW, we have a section where it's considered polite for new members to introduce themselves even before the question compelled to join.
Generally speaking you can replace a pallet stone with another of the same width, and that has been shaped for the appropriate side of the fork (entry or exit). Let's say for your average vintage watch, a replacement stone from Seitz or other assortment will probably be just fine. You do run into issues with certain escapements for higher end watches from back in the day or modern watches with higher beats and more teeth in the escape wheel; often older high end escapements might have significantly different face angles from "common", and modern escapements have very different angles for sure. Usually it's possible and normal to replace an entire fork for a modern watch. With vintage/antique it can be very advantageous to fine tune the angle on the impulse face.
One issue with replacement stones is that they are sometimes just too long overall, and need to be shortened. This is usually done on the end that fits in the fork as it just needs to be approximately squared off; I do it with a fine diamond grinding wheel (7 micron) holding the stone in a tiny vice. I suppose it could be done with a fine diamond file, but these will tend to chip the stone and while not affecting the function it is unsightly.
Hi Sonny and welcome to the forum. With the nice etching on the Waltham I'd certainly give it a go and try restore it to a new lease of life.
First as Saswatch says strip it and take lots of photos while you are doing it. Next inspect all the parts meticulously looking for broken or worn items. If you are not sure thats what this forums for ask and you will receive advice. During stripping you may come across difficulties, if so just ask for help. It would be great to see you (a) find the errors and (b) correct them and (c) have a fully functioning time piece that you have made work.