The Aurora Compressor is a Ross Compressor or MXR Dyna Comp clone with a few modifications: a treble switch to control the amount of high-end attenuation after the compression; an attack/release control that can be wired either as a knob or a switch; and an internal trimmer that allows attenuation of the input.
This project uses the CA3080 OTA, which was obsoleted in 2005. There was still plenty of old stock available, but then a company called Rochester Electronics purchased the fabrication equipment from Intersil and began producing it again, primarily for the hobby & repair industry. These days, if you buy a CA3080 from Small Bear Electronics, you will get a new-production CA3080 from Rochester Electronics.
At $4.95 each, they aren’t cheap, but if you need them in any kind of quantity, I’ve had very good luck buying them from Chinese sellers on eBay in lots of 50 or 100. These are usually pulled from old equipment. You can get them for pretty close to $1.00 each. The usual disclaimer applies that there are a lot of counterfeit NOS parts on eBay, so check the seller’s ratings before ordering.
The LM13700 is a current-production OTA that can be used in place of a CA3080 in the Dyna circuit with no sonic difference, and in fact is the chip of choice in the Ibanez CP-9. The only trouble is that the LM13700 is a dual OTA in a 14-pin DIP package, so the PCB must be designed around it—it’s not a drop-in replacement.