On ebay, you can totally trust the seller known as esciguy, Ken
Diede. Use ebay’s advanced search, and enter esciguy in the “show
only items from this seller” option. Be sure to use all lower case.
Another totally trustworthy ebay seller is Don Knight, dcknightjr,
whose items are all prefixed with the searchable string DKCK. But I
don’t remember him having blue chalcedony, unless you’d settle for
Holley blue agate.
And West Coast Gems is 100% totally reliable, owns a number of mines
in the Northwest.