These were the parts that I used for the Montana install on my 2010 GS:
I got all the parts from gps city, save the BMW 3-pin connector for plugging into the factory GPS connector.
1. Garmin Montana 6xx AMPS Rugged Mount with Audio Power Cable...
SKU: MONT6MNTPOW MODEL: 010-11654-01
2. RAM Mount Steel U-Bolt Motorcycle Mount Base RAM-B-231U
SKU: RAMB231STEEL MODEL: RAM-B-231U
3. RAM Mount Rectangular AMPS Plate B-Ball RAM-B-347U
SKU: RAMB347 MODEL: RAM-B-347U
4. RAM Mount Adapter for Handlebars (Item 2 contains one of these, but I ordered anyway b/c I didn't know for sure and it was cheap)
SKU: RAP319 MODEL: RAP-319U
5. RAM Mount Locking Knob Brass Thread for 1 inch Socket Arm (not necessary, but I like that I can adjust with no tools and can lock the mount as well)
SKU: RAMKNOB3L MODEL: RAM-KNOB3LU
6. RAM Mount Short Arm B-Socket RAM-B-201U-A
SKU: RAMB201A MODEL: RAM-B-201U-A
7. BMW Accessory Plug Connector (straight from the BMW parts catalog)