Analog computers weren't built of TIP120s or LM386s or 2N2222s. They were built with 12AX7s and 5U4Gs, and the later ones of Philbrick K2-Ws. By the time the TIP120 came out, DEC was building PDP-11s out of TTL chips. TTL is rather dumb nowadays, as we have CMOS.
One thing is true about the old parts, though... you can still buy them. I've had occasion to work on some 15 year old electronics, and none of the bigger chips are made any longer. We can still get 741s to fix our 40 year old spectrometer, but no Xilinx 4003s to fix the 20 year old one, nor CoolRunner CPLDs to fix the ten year old one.