I have a 1992 Hot Spring Highlife which needs some new flex hose. The inside measurement of the hose looks to be 1 3/8". I can't find this size anywhere for purchasing; does this sound right? We don't want to have to replumb the entire tub. 1 1/2 ' looks to be the standard hose size. Anyone encountered this problem and any ideas/solutions would be much appreciated as we are at a loss of what to do next.

That's standard 1.5" flex. You can get it in many hardware stores, home depot, lowes, etc...

or here:
http://spapartsnet.com/Spa-Replumbing/F ... Vinyl-Tube

splitting in the hose is common to older spas and especially ones that have seen freezing temperatures. You can either splice or replace the bad sections, but be sure to use flex pvc cement and appropriate primer/cleaner

they're right. I can help you with any OEM stuff in the future. Good Luck!