Robert,
You should be able to get these through Cisco.
2600 part numbers:
ACS-2600RM-19= ACS-2600RM-19=, 19 INCH RACK MOUNT KIT FOR THE CISCO 2600 SE CUR 1
ACS-2600RM-24= ACS-2600RM-24=, 24 INCH/23 INCH RACK MOUNT KIT FOR THE CISCO CUR 1
3500 part numbers:
RCKMNT-3508= RCKMNT-3508=, REINFORCED RACK MOUNTS FOR THE 3508G XL NPI 1
RCKMNT-3548= RCKMNT-3548=, REINFORCED RACK MOUNTS FOR THE 3548 XL NPI 1
RCKMNT-3550-1.5RU= RCKMNT-3550-1.5RU=, RACK MOUNT KIT FOR 1.5RU CATALYST 3550-1 NPI 1
Hope this helps you,
Don