Check Amazon ! I bought several 2 piece jaw 6" chucks from them last year. That one is not available right now. They do have a 6" one piece jaw one for about $90. Also try CME-Shars-Discount Machine on eBay. SANOU was the brand that I got on Amazon, surprisingly good on runout. And at the time was about $100 with free prime shipping.
T.L., I have a heavy 10 also with an L00 spindle. I bought a Sanou 5C collet chuck and backplate that has worked very well for my uses. Just FYI. (just so you know, I am not a great fan of chinese stuff, but the fit and finish and runout are good, and it was at what I thought was a reasonable price) Merry Christmas. Jim