I think there is some confusion here. The RC5 protocol specifies the modulation frequency as 36KHz, and that is the frequency used in nearly all universal remotes for RC5 signals. There is some variation among remotes, but I would expect that any universal will transmit within a few percent of 36KHz. So you should be able to find these in local shops.

But that's not the whole story.

The RC5 protocol allows for 32 device numbers, and 64 command numbers (128 in the RC5x protocol). RC6 looks almost the same, with 36KHz, but the lead-in part of the signal is different, and it offers 256 device numbers and 256 command numbers.

Most universals can send only a few of the 32 (or 256 in RC6) possible device numbers, and also a limited subset of the command numbers. Newer OneForAll brand remotes can send (after manually programming each button of the remote) all possible device and command numbers for RC5.

Are you sure that you need RC5 and not RC5x or RC6? Do you know which device and command numbers are needed?