This is a thread regarding the seat heater, which includes the part numbers.
The lumbar support is a rather complex mechanism that could be very expensive to replace as an assembly. I couldn't find a part number for the whole mechanism, but I did find a TSB regarding the lumbar support being too hard that has diagrams that may be able to help you.
Bulletin No.: 02-08-50-009
Date: November, 2002
Front Seats Uncomfortable/Hard In Lumbar Area
(Install Low Tension Spring Assembly)
2000-2002 Buick LeSabre
2000-2002 Pontiac Bonneville
2001-2002 Oldsmobile Aurora
Some customers may comment on the hardness of the front seat backs and that the seats are not comfortable in the lumbar area.
This condition may be due to a high tension spring assembly in the lumbar support system.
Replace the existing spring assembly with a new low tension spring assembly, P/N 88895714.
1. Adjust the front seat assembly'* lumbar control to the maximum rearward and maximum downward position.
2. Open the seat back cover in order to access the lumbar support assembly.
2.1. If applicable, remove the 2 screws located at the bottom of the J channel fasteners (2, 3).
2.2. Disconnect the double J channel fastener (5).
2.3. Disconnect the J channel fasteners (2, 3).
Important: Do not remove the existing spring assembly at this time.
3. Hold the new spring assembly in your right hand and insert one end through the LH hole of the lumbar support yoke bar (4).
4. Use your left hand to squeeze the top portion of the black lumbar basket (1) and the metal support frame (5) together.
5. Insert the other end of the new spring assembly up through the oblong opening (3). Let the hook rest over the basket edge.
6. Remove the old spring assembly by cutting the wire with a pair of diagonal side cutters.
7. Insert the hook end of the new spring assembly into the round opening (2).[/url]