I don't think the government has many M416s left. Last time I was at Camp LeJeune, NC, they had a fairly big fenced in lot full of M151 Jeeps most with less than 1000 miles on them and M416s that were scheduled to be sold for salvage. That was back in the late 90s. I doubt they have any left now and watching the same government website, it is rare to find the small M416s at all any more.
I did own a 3/4 ton M101 which is an awesome trailer. At one time I hauled nearly 2 tons of stone in it and barely got my XJ stopped at a stop sign due to the weight. Its a bit larger than the M416/M101 Canadian 1/4 ton trailers but it is a work horse. Have thought about buying a decent one due to how cheap they are and to see how it might work as an off-road trailer. It certainly will carry more gear and I pulled one cross country with over 1000lbs in it with my Scrambler, no problem. I might point out that my Scrambler had a 360 AMC V-8 which really makes a difference.
If I remember correctly my 3/4 ton M101 was about 5' wide (about 6" wider then the 1/4 ton trailer) and about a foot longer at around 7feet bed length. The wheel wells are in the trailer rather than wide finders with the wheels outside the trailer like the smaller trailers.