Oh sorry - it's a well-priced, trendy clothing store we have here (Montreal, Canada). But I know they are in the States as well. I believe they are a swedish company. If you want to see them go to shop.hm.com which will bring you to their site. However, it's in swedish or german or something. Click on "BARN" at the top (must mean kids) and then select Bad/strand from the middle column (must mean bathing suits!). You will see the spiderman and spongebob model on the photos (listed as Badbyxa). You can click on the photo of the boy wearing it and it will bring you to a more detailed info page, where again you can click on the swimshorts to enlarge.
I actually find that they look a bit shorter/tighter on the boy model than they do on my son. That may be because I opted for a larger size. I don't know. But mine seem longer and looser (not as skin tight). Also I was able to find the same type at a different local store, and their models were longer - mid-thigh I'd say. I know they are more of a european looking type suit. But to be honest my DS6 couldn't have cared less. He was just happy that this solved his problem. After enduring that burning pain, he would have worn anything, I'm sure. And we didn't know anyone else there anyway (except our friends whose son had the same suits for the same problem). My SIL didn't believe me about this, but boy was she happy last summer when we were in Wildwood and I had a few she could borrow for her son, my nephew. No more ouchies!
I know they may not be the "look" you love (kinda 70's), but it works. And quite frankly on "my" son I actually find them adorable!

He looks quite athletic and kinda like a little olympic swimmer. I only use these when we are at the beach for extended days such as vacation. This is not usually a problem for us if we spend one day at the beach. It's only when we have several days there that the irritation develops. For the one-day beach or in the swimming pool he always wears the standard long board shorts.
Anyway, hope this helps. Not that you can order online from them, but you may be able to locate a store near you. Or at the very least know what you are looking for.