Personally I wouldn't buy used M3 shocks, at least if you found some Bilstein sports you could have a chance of warrentying them once they're worn.
Plus with the H&R springs the sturts aren't going to last long anyway, you might just want to wait and get something valved tighter for the uprated springs.
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."