I've been using Waytek Wire in MN for years. Copper is going through the roof though. They have an online catalog and you can buy from them with a credit card or debit card. Try: waytekwire.com. Terminals, relays, terminal boards, everything. It takes a bit of searching but it's there.
I use the tinned Marine cable. No problems with corrosion and it carries a lot of current.
My Two cents.
Bob