There is a sailboat wrecking yard in Bellingham that often posts on Craigslist and which has tons of masts. Here is their website:
A San Juan 21 mast (it looks like they have a SJ21 parting out) is only 6" taller than the Cal 20 mast and will likely fit. Just get the mast step as well (and the boom too). The boom is a little too long, but that is easy to fix with a hacksaw.
Getting the boat operational in the next couple of weeks while you move seems complicated.