In Canada, Apex Keyboards. They just sold out of a batch of Alpacas yesterday (?) in about 3 minutes.
They have Silent Alpacas up for pre-order right now, and I think PrimeKB does in the U.S.
PrimeKB seems to be a regular retailer of them in the U.S.
Also, you can order them off AliExpress from the Durock Store as their L-series linears, but shipping can be an iffy proposition. The ones I ordered in April still aren't here yet.