It is not that easy to find a good replacement OP in a DIP package.
At least for some of the OPs one could use µA741/LM741. OP07 could also work work though relatively slow and thus not so good for the current regulation, but definitely OK for the reference part.
TLE2021 could also work, though hard to get in DIP.
LF411A could also work. The A version is also rare through.
In the kit it is actually only the OP for the voltage regulation that really needs the high voltage. So one could bodge in some voltage reduction for the other 2 OPs.
There are quite a few tasks about that supply. There is a little more than just replacing the OPs.