I was camping over the weekend and noticed that another person had a MSR stove running on a butane cylinder.  He said that the butane was setup via an adapter for the normally liquid fueled MSR stove.  I have two Whipserlite Internationals and wanted too look into picking up an adapter kit for butane but haven't found one...anyone know of something on the market?  thanks

Not sure of an adapter. I know the international was upgraded to the "universal" which is the dual fuel type. I would contact MSR directly and see if there is a retrofit kit or if it can be upgraded at all. I not at least you know what to put on the buy list next.

I upgraded from an MSR Pocket Rocket to a Micro Rocket in my pack and have the pocket rocket to the wife. It might be more cost effective to have 2 stoves if the retrofit is too expensive. The pocket rocket can be had for around $30 and the Micro around $50.

Having two stoves might be the better solution. 2 is better than one, etc.

It's one of those you don't get something for nothing. If you look at the efficiency of the international / universal using white gas compared to a dedicated white gas stove, you will see the international  / universal is less efficient. I can only assume the same is true for canister fuel.

From MSR Website:

Water boiled per 100 ml of White Gas Fuel -

Whisperlite = 5.1 liters
Whisperlite Uni. / Inter. = 4.4 liters

Whisperlite is approx. 15% more efficient. That is easily one additional meal per liter.