Paul, I'm not sure about availability of parts, but I'll tell you what I can. The Steeldon case is described in Hamilton Service Bulletin 201-D. I can make you a copy if you drop me a note.
As you suggest, the bezel has one gasket and the crystal has another. The movement is removed through the front of the case after removing the bezel. For the Steeldon, the crystal itself is Hamilton material no. 710 and the crystal gasket is material no. 711. The bezel gasket is material no. 703.
There's a slotted gasket nut in the crown which will squeeze the gaskets in the crown together, providing a better seal with the case tube. That's if they're not all dried out to begin with. Better to order a new crown with crown gaskets inside, that's material no. 709.
S. LaRose is as good a place as any to start looking for these parts.
Oh, and tell your watchmaker that the stem on this watch is a two piece stem, but it's NOT the kind of two piece stem where the crown half of the stem can be removed by pulling it out of the case. It's not a spring claw type that will pop apart if you pull it hard enough. That will bend the claws on the crown half of the stem, an you will need a new material no. 709 for sure. The stem halves will slide apart when the movement is removed through the front of the case.
[This message was edited by Mike Kearney on February 14, 2004 at 18:45.]