Yes MP requires an MP compatible interface... if that is all you need you can find those used cheap... as long as a driver is available to run on whatever OS you are using.
There is no such thing as “LE” any more, it’s “Pro Tools” (replaced Pro Tools LE) and Pro Tools Ultimate (Replaced Pro Tools HD). And MP anything has long gone (replaced in part by either Pro Tools First or Pro Tools).
Your MP license may still help you. But I have no idea if Avid will still agree to replace a license on a *missing* iLok... Pace/iLok can replace a license if you have a dead iLok with the license on it. - it’s unclear why you need to “RMA” anything here - why? Is it broken? Or lost?
Your license options are here:
https://www.sweetwater.com/insync/pr...-upgrade-chart
And I would strongly suggest calling Sweetwater sales.
The real issue you will face is not getting a license, it is making sure you have a compatible combination of interface/interface driver version/OS version/Pro Tools version. The sales rep should be asking you lots of questions about that.