I've been curious about whether JB Weld is actually that much better than regular epoxy for a while. We have a lot of lore about that, but there are reasons for doubt.
Data is scarce. There is a seemingly genuine data sheet here:
https://www.aeroelectric.com/Mfgr_Data/JB_Weld/JB-Weld-Technical-Datasheet.pdf . It repeats the main website's claim of 500/600F continuous/intermittent max temp, but doesn't give Tg (basically the softening point). Instead they quote an ASTM D648 deflection temperature of 102.5F. That is practically room temperature and is not a good proxy for a Tg rating; showing that but not a Tg could be an obfuscation.
The JB Weld tensile strength is given as 3980 psi, which is poor at about 40% of the value for Aeropoxy etc.
On the MSDS, (available at
https://www.jb-weld.co.uk/images/technical-data-sheets/Steel_Reinforced_Epoxy_Twin_Tubes.pdf, the decomposition temperature is listed as ">220 C (>428 F)" which is lower than the claimed max continuous operating temperature. To me, the inconsistencies and lack of a Tg spec raise a red flag about the marketing claims. Genuine, documented 500F Tg epoxy like Cotronics is extremely expensive and I think there is zero chance that JB Weld is actually in the same league.
Anyway, back directly to topic, I think you could use just about any reasonable epoxy for retainers. They are only exposed to significant heat for 10-20 seconds before ejection, and the ejection event is a single (possibly double) pressure impulse. And it starts to soften at Tg; if it got brittle there would be more cause for concern. For 75mm and up I recommend the flange type retainers.