Dave I bought those Thai ones as plants at Lowe's a couple of years ago. I do see them occasionally there, but I've only seen the bulbs for sale at McLure & Zimmerman. www.mzbulb.com
They had a few interesting Thai varieties, and I'm pretty sure they had 'The Pearl' last time I looked, but they only sell them in the spring. Their fall catalog is sitting right here on my desk, no Caladiums or EE's listed. (they usually have a few interesting EE's like C. Nancy's Revenge and Blue Hawaii in the spring, too)
Btw, that particular one has 'sisters' that are very similar, one called Siam Moon, and another Thai Noon.
There's a lot of hybridizing of Caladiums going on in Thailand, and possibly not much control of registration for names.