and it is a lot of fun building them...
My first was 2 sheets of 8mm ply (sandwich - in Hebrew) I got the cheapest kind; but broke it first day out. Tehn fixed it with Polyester and some fibreglass, and it is still alive, although much too heavy.
Second board I coppied the Bat board Twin Tip - some US company. I used 2 layers of 4mm ply, with fibreglass and polyester in the middle, then 2 layers of fibreglass and polyester on the top and bottom. Also turned about a bit heavy, but I used it for a long time, before moving to Loose boards.
Anyway, all the above people already told you where to get the wood. Any wood factory, or carpenter. There are many thicknesses, and usually you stick two layers together to make the rocker, but I have heard of people using one piece and bending it by soaking it in water and then letting it dry out... There is lots of info on the net - even in the main forum, you will find guys that build all sorts of things.... I got the wood in Netanya.
I used Polyester instead of Epoxy. They say it is less durable, but for home made boards, unless you are getting really good, Epoxy is a lot more expensive than Polyester. I bought Polyester in 2 liter cans in Tambur. You get the Hardener (MAKSHE) and a catalyst (something that makes it go quicker)... I did see it also in Home Center qnd ACE, but not in the 2 liter cans, and without the catalyst (for faster reaction and setting).
I did have a number somewhere for Epoxy, but I have no idea where I put it, as I never bought any, but I did call, and remember that it was almost 3 times as much as the polyester. If you want the number, go to Musa, in Herzliya - he builds Surf Boards, I think he gave me the number. It is in Kvar Saba somewhere, where they sell the Epoxy...