But those magic crystals are so sensibly priced! They could have charged 10x and the true-believers wouldn't have thought twice about it.
That 741 kit is an educational tool, of course. Nobody proposes that a discrete retro-discrete implementation of that antique design is practical. Even if you implemented it in a DIP package.
OTOH, the pro audio world has a major case of retro-philia. Back in the mid-20th century they were making 1.25 inch square potted modules of discrete op-amps because the monolithic products at the time (the 709 and 741 typ.e parts) had major problems with high-quality audio. So API (Automated Projects Inc.
http://www.apiaudio.com/) started making the 2520 module in the same form-factor as the modules used by the analog computing people back in the day.
API is still selling audio gear, but I think they have moved on from the old discrete opamp modules. However you can still buy clones and even kits from companies like CAPI (Classic Audio Products of Illinois
http://classicapi.com/) and SLL (
http://www.scottliebers.com/)
And a highly respected home-built mic preamp (John Hardy,
http://www.johnhardyco.com/) still makes his own 3rd generation discrete audio op-amp, the 990, designed by Deane Jensen of Jensen Transformers. (US Patent #4,287,479) Last year Mr. Hardy was forced by parts availability to finally switch to SMD construction to continue using the SSM2212 super-matched transistor pair that is the heart of the design. He publishes a very interesting and comprehensive document about the 990 discrete opamp. Recommended reading:
http://www.johnhardyco.com/pdf/990.pdf