First, I'd be wondering why the fuse blew in the first place, could be a problem with a bad tube or a short to ground. You could damage your amp if you just keep replacing fuses.
There are two fuses, at least on my OTS, one is a 1/2 amp fast blow which is underneath the chassis on the left side near the power transformer, it is a standard size fuse, the other on the back panel of the chassis is a 2.0 slo-blow fuse and it is the shorter size fuse. Both were available at Radio Shack.
Thanks for the help! Yes, I wondered why it blew also. My apartment complex had a power outage the night it blew. All amps are surge protected but my OTS is the only one that went down. She'll be off to the shop once payday comes.