On the vintagebmx.com site (tech & restoration forum) there are a couple of threads about Mongoose decals. Mongoose repro decals are now available for the Motomag, with other models to follow (though no mention so far of the Californian). Another thread is specific to the Californian, and talks about the difficulty in finding decals at a reasonable price. Some people are making their own. Have a read, it's interesting. I took an interest because I might try and recreate my first BMX someday...
I like the pic gmac, it brings back memories. I remember the complete bike arriving unbuilt in a box, and being so keen to get out on it.
I might even try and track down my old one, I remember who I sold it to, but would they still have it? I doubt it...