Finding 507 isn't really an issue. The issue is the price. SLX Professional is sold at my VW dealership for a bit over $11 a liter. M1 ESP is $8 a liter at PepBoys.
I thought I had struck gold with the recent PepBoys sale of M1 for $4 a liter. Problem is, PepBoys was only selling the basic grades at that price and not ESP. (oh well, purchased 12 quarts of 0w40...which is 502 spec'd....for the Passat for $48!!)
Anyway, my hope is that 507 prices will come down over the next couple of years as I take advantage of my FREE VW oil changes....(also have a voucher for a free change at 40k miles). The first change I will have to "shell out for" will be at the 50k mile mark. By that point, I hope I can find some $4 liters of 507 to stock up on.