Olympic Weights
I was following that one on eBay. You did pretty well on it. The Aluminum uppers are certainly harder to come by. These don't seem to come up for sale very frequently and I've only seen them sold alone without the lower weights. You may have a problem finding just the lower two steel weights.
S&W catalogued these weights independently meaning you could just purchase the upper if thats all you wanted.
Part# 6604
Counterweight upper section (aluminum) 3 oz
Part# 6605
Counterweight upper section (steel) 7 1/4 oz
Part# 6606
Counterweight middle section 4 1/4 oz
Part# 6607
Counterweight lower section 4 oz
Part# 6608
Counterweight nut
Part# 6609
Counterweight screw
And S&W catalogued the complete sets:
Part# 6610
Counterweight assembly with steel upper section Part#6605
Part# 6612
Counterweight assembly with aluminum upper section Part#6604
The lower weights over the course of production essentially look the same with a dull blue finish. The difference is how they attached together. The early sets used two sets of screws to attach together and can be identified by looking at the bottom of the lower weight and seeing a total of 4 holes with two of them containing the 2 screw heads.
Later production weight sets are attached with one set of screws to attach together and can be identified by looking at the bottom of the lower weight and seeing 2 holes with only one containing the screw head. I'm not sure exactly at what year of production S&W made the change but I believe it was in the early 60's.
Members smithfan4152, TOM BECKWITH, and civil1977 are in my opinion the forum experts on Model 41's so they may have a source where you can acquire a set of original lowers. Since I've never seen a "fake" set I'm not aware of the differences in appearance. Olympic Weights period are very seldom seen in my parts.