hi finyl vinyl,
if money is not an issue you could look at importing these layered wood designs floating around on ebay.
301 garrard plinth, Electronics. Great deals on eBay!
they make for both 301 and 401 on order if you ask i think. i was looking at one of these myself, the $120 one for starters.
for plinths i have not yet come across a plinth made from either material. because most are layered plinths (usually wood) and not solid block.
for my end plinth i am eyeing the slatedeck plinths made of slate :licklips:
if you're looking to custom make your own plinth do choose a layered wood, from what i've read, a sort of plywood structured wood if you can get what i mean

is ideal. birchwood seems to be first choice for many. there was a hong kong guy who made a plinth from the slatedeck guys out of granite. this was a single slab with the cutouts for the garrard and arm.
then there's the shindo plinth
regards