I purchased a light weight 1242AG AP (AIR-LAP242AG-A-K9) when I should have purchased the autonomous IOS version (AIR-AP1242AG-A-K9). I know I can load a previous version IOS with a TFTP server. How do I acquire an IOS release 12.3(7)JA or earlier?
Hardware is same. You can convert LAP by upgrading an autonomous image on it.
After convesrion, your LAP would work normally like an autonomous. But, if you ask for a replacement in future (due to any h/w issue on AP), you will get the LAP as a replacement from Cisco, as upgrade would not change the model number.
Please see the folloiwng link to change your LWAP to autonomous mode: