Turning Radioactive Blue stale is not as difficult as you think.
Even when hunting at the Catacombs or the Mousoleum, you're bound to make a Radioactive Sludge or more.
Not enough Radioactive Sludges when it's time to make your Horrific VMT?
Simply choose your trap combination with the worst cheese effect available to you (like Acronym + Explosive Base). Head on over to a fast and furious area where most/all the mice are not attracted to RB nor your trap type (Acronym/Arcane). This could be the Furoma areas or the Bristle Woods areas.
Remember to monitor it or you'd burn more RBs than you really want to - there's not much use for Sludges at this time, so no point farming more than what you need for making the traps.