I've been trying to track down the o-ring sizes for the Blichmann Boilermaker pots and all I found online were other people asking the same question. When I emailed John the response that I (and others) got was that they're sold by various vendors. Not wanting to spend $6.99 a set for my 4 pots, I took one apart and measured them. Here are the equivalent McMaster-Carr parts. There are 5 different sizes, 1 size is the same as what the Corny keg posts use, so you may already have some.
BrewMometer: 9396K24 $10.71/100 (Same as Corny keg posts, site glass top and bottom furthest from site glass)
OuterValve: 9396K66 $10.90/100
Inner Valve: 9396K25 $11.42/100 (Same as site glass top and bottom against pot)
Site glass block (4 in each block)
Top and bottom clean out: 9396K17 $5.69/100
Top and bottom against pot: 9396K25 $11.42/100 (same as inner valve)
Top and bottom closest to site glass: 9396K26 $11.44/100
Top and bottom furthest from site glass: 9396K24 $10.71/100 (Same as BrewMometer and Corny keg posts)
For a complete set, order:
Total cost is $46.43 (same price as ~7 replacement sets) for 33 replacements ($1.41 a set) with 17 extra 9396K66, 9396K26, and 9396K17(probably the easiest to lose).
42 Gallon Conical 42 Gallon Fermenator
Racking Arm: 9561K31
Bulkhead fitting for Tri-Clamp models: 9557K156 (1 3/8 OD) or 9557K158 (1 1/2 OD)
1/2 and 3/8 Quick Disconnects: 9396K208 $7.31/50