There are certain items and berries that have similar effects, I believe, but they are difficult to acquire and would only work once, against a single type. The Christmas market in Goldenrod would be your best bet for those.

[It sure sounds like it always comes down to levels or money, doesn't it?]

There is nothing stopping you from challenging gyms in any order. You could even start with Blackthorn, if you wished. But do note that the trainers' and leader's team levels are set; a later gym's type may be weaker against your bugs, but they'd still be much stronger by default.