Best place to buy CYA

Need to buy some CYA for my pool as it's current less than 30... Any recommendation where to buy it?

Also, any recommendation of Powder form vs liquid form?

I buy mine at a local professional cleaning supply store. They sell pool chems for less than the local "pool stores". You might check around and see if there's something like that in your area.

I buy CYA at Lowe's. It's 100% CYA and comes in a granule form.

I only need to add small quantities of CYA and do so by adding 99% dichlor that I bought at Sam's Club. (Guru-Ben's recommendation). Adds CYA and FC in manageable quantities and is readily measurable.