I know where you can buy a Caterpillar battery in Medford, Oregon, but I doubt it'd make much sense to buy it up here
Our tractor dealers carry the batteries to fit the tractors they sell as well as cars and trucks. You might check your nearest Caterpillar dealer, which is probably Hawthorne Machinery (based on the lookup feature on the Caterpillar site). There is also an "application" guide online at the Caterpillar site, if I remember correctly, so you can get the appropriate part number. I don't know how much they are, but if you need a good battery you might also ask Blaine about the Odyssey line.
Also, not all Costcos are carrying the Red Top (or any other Optima). It's a regional thing, just like our Costco here has to special order BFG ATs, but has tons of BFG MTs in stock. Signal Hill (Long Beach) had to special order the MTs but had ATs in stock. The Kirkland (Costco) brand battery is made by the same company that owns Optima, although the Kirkland and Optima batteries are not the same battery.
Áron O'Proinntigh is ainm dom