I go by Effective Top Tube (ETT) over Seat Tube when finding a bike that fits.

If you need a lot of reach, get an XC bike.

For instance, the Fredly Tral bike Trek 820 mentioned earlier comes in a 22.5" but its ETT is a measly 60cm.

My 19" KHS's top tube is 60cm. Trek's current crop of 18.5" XC bikes have 60.7cm top tubes. Their 21.5" XC frames have an ETT of 64cm. That's a pretty big bike!

If you want a frame that's bigger in the height department there are plenty of long seatposts, 3" riser bars and angled stems to choose from.