The stand turned out nice, good job.
Regarding garden mat equivalents, I wouldn't use yoga mats. At least not the ones I saw. They were very weak, nowhere near as dense as the ADA mat. Maybe it doesn't matter, but I wasn't comfortable with putting my tanks on it. They'd flatten those things out to be paper thin under the weight of the water.
Not sure what these drawer liners are?
The best and nearly identical material I found was a quality high density neoprene. Black, durable, feels almost identical to the ADA stuff. I had to buy in bulk to get the stuff. I got some 10mm and 6mm material. If you don't find anything to your liking I could sell you portion.