I dont know if napa would have it... if they do it will be like a freaking 5 gallon kit for cars!!! and you will pay for 5 gallons! try a motorcycle shop. or if you have a "warehouse paints" near you, they will have it. i have heard of red kote, kreem all those are basically the same. and insoluble sealer. i use por15 because it is local to me. one note.... MAKE SURE YOUR TANK IS COMPLETELY DRY before pouring in the sealer. also... since you said you already poured oil in there you will have to acid clean it again before you coat. sorry but you have to re clean it out now!
most kits will have the cleaner the acid and the seal for like $50. you can run what you have just be cautious of the condition it is in now. if its not too bad you may be alright. hope that helps man