What year air suspension bags will Fit?

If you want, with the right tools, you should be able to replace them yourself. I've heard Strutmasters are pretty good:
http://www.strutmasters.com/Lincoln-Town-Car-Rear-Air-Spring-Assembly-p/-smltc-as.htm

And then there's these guys:
http://www.suncoreindustries.com/lincoln-suspension/towncar/1989-2011-rear-air-spring-bag.php

Full warranty on both.

REAR ELECTRONIC SUSPENSION SYSTEM -1997 Lincoln Town Car Cartier
Page 1 of 2
AIR SPRING

Removal

Turn off air suspension switch, located in right side of trunk. See Fig.
Rear suspension is at full extension. Remove heat shield (if equipped). See Fig. 19.
11
1.
. Raise vehicle on hoist so
Fig. 19: Identifying Air Spring Components Courtesy of FORD MOTOR CO.
WARNING: DO NOT remove air spring under any circumstances when there is pressure in air spring.
Remove spring clip. Remove air spring solenoid. See AIR SPRING SOLENOID
piston-to-axle spring seat by inserting Air Spring Remover (T90P-5310-A) between axle tube and spring seat on forward side of axle. See Fig. 20.
3. Position tool so its flat end rests on piston knob. Push downward, forcing piston and retainer clip off axle spring seat. Remove spring from vehicle.
. Remove spring
2.
Fig. 20: Removing Air Spring Courtesy of FORD MOTOR CO.
Installation Precautions

DO NOT install or inflate any air spring that is unfolded. See Fig. 21
Any unfolded spring must be refolded before being installed in vehicle. DO NOT try to refold air springs which were previously installed on vehicle and not folded correctly.
When installing a NEW air spring, DO NOT apply load to suspension until springs are inflated. See AIR SPRING FILL PROCEDURE. After air spring is inflated in proper position, ensure it has
correct shape. See Fig. 22.
1. 2.
.
3.
Fig. 21: Folding Air Springs Courtesy of FORD MOTOR CO.
Fig. 22: Correct Shape Of Installed Air Spring Courtesy of FORD MOTOR CO.
Installation

See INSTALLATION PRECAUTIONS
spring seat, taking care to keep solenoid air and electrical connections clean. Attach push-on spring retainer clip-to-knob of spring cap from top side of frame spring seat.
Attach air line and electrical connector to solenoid assembly. Attach heat shield to frame spring seat if required. Align air spring piston with axle seats. Increase pressure by squeezing and push downward
on piston, snapping piston to axle seat at rebound. It should be supported by shock absorber. Refill air springs as outlined in AIR SPRING FILL PROCEDURE.
Install air spring solenoid. Install air spring into frame
REAR ELECTRONIC SUSPENSION SYSTEM -1997 Lincoln Town Car Cartier