What amp, and where exactly in the circuit is that cap?
In general, in rough terms increasing the size of the cap will either let through more low-end or bleed off more treble, depending on what it's doing in the circuit, apart from cathode caps which have the opposite effect (although from the value, I wouldn't expect it to be a cathode cap.)
Depending on what it's doing and what (if any) resistance is in parallel with it, you could get an effective change by going to 3300pF, or possibly not until you increased it tenfold (22000pF/.022uF).
I would stick with the same type if possible, and certainly with at least the same voltage rating. Most of the online sellers (eg Mouser) have a good range in all types.
If all that sounds too complicated, you could actually just add more or less any cap across the output of the reverb tank. Again, the value will matter - too small and it won't do anything, too large and it will kill the reverb fairly dead - and I can't easily say where to start without knowing more about the amp, but even a dozen different values of small ceramic caps won't cost more than a couple of dollars. In this position the type and voltage rating won't matter and there's no risk of messing anything up.
