Hindsight is 20/20 and if you knew you wanted to run an ISCG chain guide when you bought your last bike you would have ensured that it had the appropriate mounts. Well, don't fret my friend. Use a MRP Non-ISCG Adapter and you're in business. It will mount along with your bottom bracket, take the place of your drive side spacers, and give you the ISCG mounts you have been looking for.
Adapts BB to ISCG-05
Maintains original chainline
Manufacturers Part Number: MR-21-2-045
Mountain Racing Products (MRP) produces chain guides for extreme mountain biking. Their products have a high regard and are extremely popular, with models to fit a wide range of frames the World over.