[Moved & Updated]
Investigation revealed that there are a couple of possible drop-in replacements for high insulation reed relays K307-K312 .
Even if there would be cheap salvaged parts awailable, better to be suspicious if they are untested and sold without any warranty.
-Original brown/black E-T R7526-1 (Keithley-Part# RL-70 - same as Coto 1240-0197, e.g. Keithley 617 < Rev L, 614): no source, no datasheet
Rcoil=600\$\Omega\$
-Coto 1240-0197 (Keithley-Part# RL-70, e.g. Keithley 617 >= Rev L, 199):
Ebay (NOS) - 60$ (ask for stock & delivery outside us): Very high insulation resistance, 1FA, 350V, 0.35A/2.0A,10W Instrumentation Reed relay with an electrostatic shield and a 5V, Rcoil=625\$\Omega\$
No direct drop in:
-Coto 1203-0147 (Keithley-Part# RL-181 - same as ARI 300RCA - no datasheet found, Keithley 6514 & 6517 EM, 6521 & 6522 scanner cards):
awailable from Keithley/Tektronix (spare-parts: web-form) - ~50$spacing ES-Coil tighter
-ARI (
American Relays?) SO051A 300RCA (Keithley-Part# RL-181 - no datasheet found,
6514 EM(at least from week 37 2008),
Keithley 3761 scanner card): awailable from Keithley/Tektronix (spare-parts: web-form) - ~50$
Rcoil=300\$\Omega\$, spacing ES-Coil tighter
-
Coto 1240-06-2104 (active part - confirmed by Coto, 1E14\$\Omega\$, 6V/5V compatible, RoHS): several sources, but ~100$
Rcoil=150\$\Omega\$
Other high insulation resistance reed relays:
-
Okita TRY-105SV-15 (1E15/1E14\$\Omega\$, E/S-shield, 350V, 1/2.5A, 50W, 0.1pF, 50µV t-EMF) - source?, price?
Similar relays are used in
Advantest R8340A Picoammeter (
TRY-104S)
-
Sanyu 95D-1A14N4 (1E14/1E13\$\Omega\$, E/S+M-shield, 350V, 0,5/2,8A, 50W)
distributor, ~25$
-
Standex-Meder HI-Series (mentioned by branadic, cheap: ~15$): no ES-shield (
to be handcrafted - razberik), only 1E12\$\Omega\$ (Model 66) / 1E13\$\Omega\$ (Model 85) [Coto 1240-06-2104: 1E14\$\Omega\$], t-EMF? - preferred HI 05-1A85, but seems not to be awailable