Are 2.73 gears hard to find?

[Ardenq]

Hey guys, poked around the site and finally registered to get some info I couldn’t find searching.

I have a 68 c10 with 250 and 3 speed and an open, I’m told they came with 3.73 gears but I’m not sure (they’re likely stock based on the rest of the truck).

I’m looking for a high gear set for a big block swap but 3.08 is the best I could find.

It looks likely they made a series 2 carrier, is that hard to find? I couldn’t find any info for 67-72 trucks.

If I have a series 3 I “should” be able to run a used set of 2.73 gears. Are they only square body c10’s?
A used set of gears and a series 3 posi and I should be all set?

After looking through craigslist, the classifieds and eBay I didn’t see a lot of options, are they in demand, or is it one of those things guys don’t really sell because there isn’t a market?

Going with big block/auto and want to keep the trans I have.

Thanks for any info,
Arden