I haven't located this spring either. My truck is a 2001 Ram 2500 with a NV5600 and HO Cummins. It sucks not having a functional parking brake, especially in a cold weather state with an inclined driveway.
I recently learned this spring may have been used in some other Chrysler vehicles. The details on the spring and the other vehicles you might be able to get it from at your local junk yard below.
Here's the info I found about the spring:
Original Part Number = 05010008AA.
Seen on Mopar websites listed as:
-Spring. Right or Left. Parking brake cable: 5010008AA
-05010008AA = parking brake tension spring. Or 5010008AA.
My local dealer says discontinued in 2015.
Weight = 0.19
Length = 11
Width = 0.62
Height = 0.62
Measurements in inches/pounds I believe.
Part also found in:
-Dodge Ram 2500 2000-2001 10 Cyl 8.0L, 6 Cyl 5.9L Diesel, 8 Cyl 5.9L
Quad Cab 2WD, Quad Cab 4WD, Regular Cab 2WD, Regular Cab 4WD, Regular Cab Chassis 2WD, Regular Cab Chassis 4WD
-Dodge Ram 3500 2000-2001 10 Cyl 8.0L, 6 Cyl 5.9L Diesel, 8 Cyl 5.9L
Quad Cab 2WD, Quad Cab 4WD, Regular Cab 2WD, Regular Cab 4WD, Regular Cab Chassis 2WD, Regular Cab Chassis 4WD
-Dodge Ram Van 1998-2003 6 Cyl 3.9L, 8 Cyl 5.2L, 8 Cyl 5.9L
Ram 1500 Conversion, Ram 1500 VAN, Ra
-Possibly in Chrysler Sebring 1997