Do a search.

Micheal's has it here, too. Also K-Mart and Walmart, sometimes. Look in the kids and crafts sections. You never know where you're gonna find anything at Walmart. Went there once and wanted to buy some Velveeta cheese. Searched the cheese section several times. Nothing. Asked an "associate" if they had any, and was told it was in Aisle 4. I asked "Why?" Was told because it didn't have to be refridgerated......:bash::bash:....HUH???
BBBBut.....it's cheese......????? Aisle 4, sir......

PS.... Not wanting to appear like Scrooge or anything, but I try to salvage as much of the clay as I can from a bedding job to use again. It doesn't take much time or skill to pick the hardened material out of the clay. I keep it wrapped up in a piece of Saran Wrap or the likes of.

I just did a Remington LSS Mtn. Rifle with Devcon Stainless. I did not use modeling clay and had no trouble. Getting just the right amount is the trick and the only place I can see where you may need it is the barrel channel...just a head of where you want to stop the bedding material. I did the tang, recoil lug, first 1 1/2" of the barrel channel.

Things I had to have
2 stock bolts - short pieces of 1/4" fine thread all thread roughly 5" long with four nuts and four washers
2' piece of surgical tubing
roll of blue masking tape
dremel tool with cone shaped burr
black marker
Brownells release agent (other products work equally well)
a couple of clean white rags ...preferrably with no lint
black electrical tape for the recoil lug
razor knife
popcicle sticks

I also removed the contact pad in the original barrel channel. Some say leave it, some say remove it. I figured I could always make one with Devcon if I found it was necessary. It was not and the rifle is a much better shooter than it ever was.