Where can I buy 16" steel rims for my 02 disco? I have 18" on it now and want to use a 16"....?

 

Almost any of the Rover parts suppliers, also check e-bay and Craig's List and the "wanted/for sale" section on the forum.
Steelie's ain't cheap though.
You are looking at min $50 each plus shipping.
The rims from a P-38 Range Rover and any year DII will fit.
The rims from a BMW X5 will work with some modification, but personally I would just buy Rover rims.
I have heard but cannot confirm that the rims from a LR3 will also fit.

 

Keep checking ebay, took me a few weeks but scored 5 for around 200.