And you can probably find a 32-36 qt stock pot pretty easily. I bought one at Walmart that I use for small-batch, single-vessel BIAB -- my big kettle just had way to much surface area to volume and the boil off was bananas. It's small enough I can hold mash temp in my oven if I want to.
A 32 to 36 quart stock pot is not ideal for 2.5-gallon batches. The last brew house I built was a 3-gallon brew house (i.e., that is 3-gallons kegged). I would start of with 4.25 gallons of runoff from my mash tun and boil it down to a little over 3.5-gallons before racking 3.25 gallons to one of my primaries. I ended up building a totally custom kettle from a Vollrath Optio 3506 27 quart stock pot, which is 12.5" wide by 12.5" tall.
Here is the setup when I first built it (the vinyl tubing was replaced with silicone):
27qt kettle, 5-gallon mash/lauter tun, and 5-gallon hot liquor back (the perfect size 3-vessel brew house for 2.5 and 3-gallon batches, but an Anvil 6.5-gallon all-in-one is a better investment these days)
Here is the inside of the kettle, which is also totally custom:
The false bottom was used with whole hops. Using whole hops and a false bottom is my preferred setup, but using whole hops was not a wise investment with such small batches because it took forever to work through a pound of hops. Five gallons is the smallest brew house that is practical when purchasing whole hops in bulk because I formulate my recipes based on six gallons to account for losses to the kettle and the primary (i.e., I like to fill a keg to the top).