I brought my own...
In NY-State it is required to have two license plates, front and rear, as far as I know they don't tell you they have to be the same, though
OK, I'm being a smartass here...
Long Island cops don't seem to care about it, I've been driving around like this for more than three years now, got pulled over once for 'unsafe passing' and passed a police checkpoint once without getting in trouble for it. I wouldn't drive it into the city, though.
If you want to make it look 'authentic' try to get a plate from Stuttgart, the first letter is an 'S', to make it look even better, try to get a plate from that time, the design changed slightly in the mid-nineties. Older plates don't have the blue part on the left like mine.
If you need more info on how plates look over there (which letter for which town, which letters are not used, registration and inspection stickers, etc.) let me know.
BTW, do yourself a favor and don't buy one of those 'fake' german plates they sell over here (aparently to VW-people, mostly...). I think that's just embarrassing, those random letter-number combinations and the sticker that says 'Bundesfinanzverwaltung'. The Bundesfinanzverwaltung has nothing to do with car registrations. And they don't have custom plates in Germany, the first 1-3 letters always stand for the town/region the car is registered in, you can only choose the the next 1-2 letters and the 1-4 numbers. Those are the patterns, I use "T" for town, "L" for letters (some are not used on older plates) and "X" for numbers and the dash in between the letters disappeared on the newer plates:
T-L X
T-LL X
T-L XX
T-LL XX
T-L XXX
T-LL XXX
T-L XXXX
T-LL XXXX
TT-L X
TT-LL X
TT-L XX
TT-LL XX
TT-L XXX
TT-LL XXX (most common)
TT-L XXXX
TT-LL XXXX
TTT-L X
TTT-LL X
TTT-L XX
TTT-LL XX
TTT-L XXX
TTT-LL XXX