Do you have 36" for a sink or a 36" cabinet (which would give you 34-34-1/2" clearance. Either way, I suspect you are not finding them that size because the bowls would be too small to be very useful. I don't think I've seen one less than 39-42" -- unless it was something like the one below.

Here is a link that might be useful: A variation on a triple bowl

I was looking for the same thing. I found an undercounter by Franke, Element Triple Bowl Undercounter Sink - PAX on the HomeClick site, list price $1500, sale price$1125. The overall dimension is under 38". I also found a drop in sink by Instawares, Triple Drop-in Sink w/ Faucet, list $580, sale $475. The overall dimension is under 37". Hope this helps.

Thanks. I'll check them out.