I doubt you're going to find Kanthal wire anywhere in a "brick an mortar" store, unless it is a
shop that specializes in selling supplies to people who buil toasters an ceramic kilns...
The net place to get small quantities of Kanthal is EBAY. You can usually get small, lengths there (1-10 feet) for a reasonable price. Also, watch the classified section on this forum.
Several OEM-type mail orer/online stores carry it, but you usually nee to order an entire spool 50-100 feet (which is enough Kanthal to rebuild attys for several lifetimes). One thing you can o is go in with a few friends who also want to try their hand at RBAs, and split the cost.
You can actually get the stuff from Amazon:
Amazon.com: kanthal: Industrial & Scientific
and of course most vape vendors who sell
mods an RBAs sell wire too...