I don't know about HMM, but...
If HMM can export a big full resolution image, you can cut the map to any specific paper size using a graphics program like GIMP (or Photoshop or whatever).
And on the topic of GIMP/Photoshop, depending on the level of detail you want in your maps, it's not too hard to create maps from scratch using merely GIMP/Photoshop.
For example:
https://bg.battletech.com/forums/index.php?topic=64737.0 YouTube has some videos on how to do this, mostly targeting roleplaying games like D&D, although the principles are identical.
You may want to consider looking around for a PVC banner printing company.
PVC banners will hold up much better over time than prints on paper.
And in most parts of the world PVC banner printing has seen a lot of competitive pressure, so it might not be much more expensive.
And since it's printed os a single sheet of PVC, you won't have any unslightly seams to contend with...
In my experience there's only one downside to printing on PVC banners, and that's resolution, generally speaking a print on paper will retain crisp detail better.
Assuming you're located in the US, as an example:
https://www.signs.com/banners/ (I have
NO particular experience with them)
A 18x22" print on PVC would cost you about 16USD (+possibly some shipping)
Compared to a 18x24" print on paper by Vistaprint costs 12USD (or Premium Matte at 19USD). And even with two tabloid sized prints, which is slightly too small, you'd end up a 2x6=12USD (again using Vistaprint pricing).
When ordering prints on PVC, make sure to ask for a
matte finish, and don't forget to explicitly specify
no grommet placement. You probably also don't want it to be hemmed, although that's a matter of taste.