Hi Joe and welcome! In case you don't know it, HiLos are measured differently than "ordinary" trailers. The length stated is the TOTAL length, from the tongue hitch coupler back to the rear bumper. Most trailer lengths of other brands don't include the tongue or rear bumper which add about 3 ft to the total length. So, my 17 ft HiLo has a "living box" length that is about 14 ft. (That length is perfect for us since we like to camp in Forest Service or National Park Campgrounds, where the campsites are smaller and access is more restricted.)
They DID make 19 and 21 ft HiLos, which sounds like what you are hoping to find. Have patience and one will show up.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew