Can anyone suggest a place to purchase an IR Emitter with a 2.5mm plug for the MRF-250? Am I stuck using a Radio Shack 3.5mm to 2.5mm adapter?

Call

Universal remote control or contact a universal remote control dealer.

On Radio Shack's website they list a 2.5->3.5 adapter which costs $9.99. I don't know if RS stocks a cheaper adapter in the store or not.

I have used the following adapters with the MRF 250 - they work and are quite inexpensive:
[Link: hometech.com]

I don't have a recommendation for IR emitters with prefab 2.5mm ends....don't ever run into the need for them as we stopped installing the mrf-250 at least 2 years ago.

I don't recommend adaptors due to multiple connection points often lead to failures.

If you are a consumer, places like parts express, have solder on 2.5mm mono plugs which in my opinion would be more suitable.

Here's a link for you:

[Link: partsexpress.com]

If you are competent at soldering this is the best way to go.

But for those without soldering skills, an adapter is less likely to fail than a plug with a poorly soldered joint. And if the plug with adapter comes loose from the jack, it's a simple matter to plug it back in.