You will almost never find 12 volt lighting at hardware stores, at least those that will work in an RV.
The ones I have are by Star Lights, Inc. Revolution T8-18 replacement LED bulb is description.
http://www.starlightsinc.com/shop/pc...38&idcategory=
You are only going to find it in an up-to-date RV supply store--I never saw one except in a store in American Fork, UT, on my trip to CA/AK and back, when I looked. Try online is best I can suggest.
Camping World locally does not have them. Price is going to be around $45/each, tho, but last one you will have to buy. Save old bulb in case you sell the RV--and take them with you.
Joe