You can find more info, experiences, and suggestions about the discontinued through-hole and fake (or out-of-spec) LM13700 in our discussion here. In short your/our options are:
- Buy the cheap SMD version of LM13700 and learn to solder SMD into an adaptor. The IC and adapter come to a total of about EUR 1 together (around where I live at least) so it makes sense to learn the SMD soldering skill and buy in bulk if you’re going to use many of them in your modules.
- Look for new old stock from reputable sellers. These can be either large online vendors (as @analogoutput suggested) or small local shops (as I have been lucky to have around). In this case, you accept paying a premium price (EUR 3.5 to 5 in my case) and the fact that the shops will run out of stock eventually.
- Take a gamble and buy cheap from ebay/AE but test every IC before you put them in the circuit as fake/faulty ICs can cause serious damage. In the linked discussion above you can find instructions on how to build a simple test circuit on breadboard. I have also made a stripboard layout in case you can’t be bothered to set up the circuit on a breadboard (I will post it in the forum once I verify it…)
- Buy (in bulk) the Chinese through-hole version called XD13700 from AE. You might want to test those too. You are probably best testing every IC while you are at.
I have opted for 2 and 3 in the past, but 1 and 4 might make more sense if you’re going to use the IC a lot in your builds.