Where to buy open cell foam in NYC(?), and question about closed cell

I'm going crazy... does anyone know where I can find some open cell foam (AKA mattress foam, right?) in NYC? I mean specifically, not "check a craft or fabric store"?

Also, does anyone know if using 1" closed cell foam instead of 5/8" has a big effect on arrows?

I personally have never used 5/8" for arrows. Me and Chris come from Amtgard, where the archery system is a lot different. We use bows up to 35 lbs. at Amtgard, so almost double the KR limit. So, our arrows obviously need to be up to snuff on that.

Essentially, what we do is use pool noodle (about 2.5 inches worth of it), taper the end we are taping to the arrow shaft. We tape a penny onto the end of the arrow and put at least two or three caps of camp pad over that. I usually duct tape the one closest to the penny, in that way I've had the same arrows for about 2 years firing off of a 32 lb. recurve bow. I'm fairly certain if you just put some open cell on that; or replaced the last two caps with a noodle board cap, they should be perfectly legal by KR standards.

As for open cell foam, only places I know you can get it is sadly craft stores like Jo-Anns or possibly Michael's (I'll check next time I go in to work and then let you know about price, as either me or Chris can get you a discount on it if that is the case). UPS and Fed-Ex stores might also have it if there are any near you; as well as reupholstery places for couches and chairs.

Going Crazy?

If you check around the areas between 23rd street and 38th street between Broadway and 3rd Ave, you'll find places that sell textiles and other materials.  No specific store, but the area has some bead shops, textile shops, and furniture/futon places that sell material.  Home Depot on 23rd between 6th and Broadway I think also carries foam material nowadays.  Bext places for foam, plastic, and other industrial materials like that is also Canal Street and Church Ave.

I personally have never used 5/8" for arrows. Me and Chris come from Amtgard, where the archery system is a lot different. We use bows up to 35 lbs. at Amtgard, so almost double the KR limit. So, our arrows obviously need to be up to snuff on that.

KR has it's own rules and set of standards on KR ARCHERY .  I'd leave it at that and not try to compare arrows made for Amtgard for what's passable.

All I meant by that is that since I use pool noodle (so a full inch) for arrows rather than 5/8", there is more padding to it. Almost double the amount of foam. So really all I am getting at is that they should also be legal as there is more padding on the arrow shaft. But, I won't assume and will just ask a rules marshall about that one (or wait for one to post here since I don't know who most of them are yet, being a new guy).

As far as finding mattress foam goes, if you mean the egg crate-style foam pads you put on top of mattresses to make them more comfortable, I'd say look at K-Mart or Walmart.  That's where I've gotten that type of open-cell before.