Hmmmm, I don't think we have these type of shingles here in The Netherlands. A shame, because the results are fantastic!!
Just cross the border to Sauerkraut country, enter the next DIY-Store called "Baumarkt" there and ask for "Dachpappe" or "Bitumenschindeln". (I believe your county should have that kind of stuff too I guess, but here in Europe it rarely comes in shingles but usualy is rolled up in barrels).
I tried something silmilar with "Mauersperrband" (another bitouminous product also sold in German DIY stores) but that product is hard ro cut and stays sticky at the edges.