There was a small wetsuit manufacturer making suits for the urchin
divers along the Oregon and Northern California coast that went by the
name of Sealion Wetsuits.  It was really a nice 7/16" skin in suit with
nylon on the outside. I haven't seen them in a couple of years, though.
You may want to give Ol Jim at KME a call as he will make neoprene
drysuits just about any way you want them. He does a pretty good job too
... although takes a long time from what I am hearing from the shops
that send him stuff.

Good luck in your project!

Indeed. You don't have to settle for a neoprene drysuit either, the
Unisuit and O'Neill neoprene ones came along much later - the 1960s -
than the original US Divers Seal, Healthways Carib, The Spearfisherman
Frogman and Bel Aqua unlined sheet-rubber models.

I regularly snorkel off the coast here in the North East of England in
a traditional unlined sheet-rubber drysuit, made by a modern-day
manufacturer. It's ideal for cold-water snorkelling, not
over-engineered and bulky as modern suits are. There are two drysuit
models you might want to consider and they can both be ordered online:

Aquala Historical Suit
http://www.aquala.com/
The company makes a valve-less front-entry "historical suit". It's
authentic, as the Aquala/Bel-Aqua company has made such suits since the
1950s.

Hydroglove all-rubber suit
http://www.hydroglove.com
I have the green version of this suit, whose design is based on the
Skooba Totes suit, made by SoLo Marx of Ohio. I considered buying a
Totes suit in the 1960s, but didn't, and have always regretted not
making my purchase after the manufacturer discontinued the line. It
keeps me warm and I have learnt a lot through experimentation about
venting the suit and making a good seal to keep it watertight. Make
sure you get the right size and you will stay dry.

Look at the Links section of the Hydroglove site if you're interested
in early drysuits. I wrote ten monographs on some of the models that
were available in the 1950s and early 1960s and the owner of the
company kindly posted them on the website.

Ask if you want more information. I'm a "vintage snorkeller", starting
in the late 1950s like you and preferring underwater swimming equipment
as it used to be before the thermoplastic revolution.

 Gunny, I've seen what I remember to be surplus Russian (as in USSR)
military drysuits that seemed like sheet rubber to me.

 Like laminated tire rubber, and they had a big neck opening for some sort
of hardhat (?) (Matthias?).

 But they were real cheap, and you could have a standard neck installed.

 Gerard's (Gerard Underwater Educators) in Atlanta had some, but I can't
find his address anywhere.