I bought a mat, but I actually wound up giving it to a friend that wanted to start. I use only a cutting board, nori, rice and my stuffin's.
I lay the nori out on my board, apply rice and my stuffins...grab my knife. Slide it under the side closest to me...get the edge I need off the board, drop the knife and start a-rollin'. To me, by hand is easier. I can get it as tight as I need without the mat...so it becomes cumbersome for me and I don't use it. The best tool you could ever ask for is a sharp knife and some water. Dip your knife between each slice and it will help to keep the rice from sticking. Anything you dont want the rice stuck to, keep it moist. That includes your hands and your board.
Any other questions?
Unfortunately, no...I cannot recommend an online STORE, perse, but ebay is a great place to look. That can be atested to (I'm addicted!). I found an actual store about 2 miles north of my home about 1 month after ordering from the online store that didn't send my stuff. I'd given ebay a shot if you were looking online. Not so much for fish...but calrose rice (go big bag), rice vinegar and nori sheets (bigger=better for noobs).