I made my own. I had a 3x8 hyd cylinder that had a rusted rod. I took it apart and had a new rod made at the machine shop. $70 for that. I didn't need 8 inches of stroke so I cut two inches off the barrel and retreaded the four bolts so that I could put it all back together. I bought top link ball joints at Princess Auto and welded one the the shaft and the other to the end of the cylinder.
I needed to split the flow to my rear outlet. I already had the splitter. It was something that I had traded for. I built a mount for the splitter and got hoses made up and I was in business. I ran 1/4 inch lines to the top link so that the cylinder wouldn't move to fast. It all works good. I don't remember what I spent but it was fairly reasonable. If I was to do it again I would just buy a top link cylinder from Surplus Center
Check out Fit Rite Hydraulics - fitritehydraulics.com
Brian is on here frequently and a site supporter. His handle is MtnViewRanch. He custom builds them to match your needs.
Fit right hydraulics is who I was planning on purchasing from. Seems like a very nice guy to deal with large backlog though so order early if you want one.
I dont think you'll regret having one. Its awesome so much easier to adjust on the fly with my box scraper, bush hog, and even the 3pt splitter. The first 2 weigh 1300 lbs plus and are really a bear to adjust with a manual link. When i save up enough for a 3rd remote and side link i will order one through Brian
If you do any grading etc. type work...IMO you will find the the HTL will become one of the most valuable things you can put on a tractor...every time you don't have to stop and get off the tractor to make an adjustment you will thank yourself and wonder why you waited for the upgrade...
The only thing better to make operating easier would be both a top link and a tilt cylinder...
I think most all of them are double acting cylinders. There may be some single acting cylinders purpose built but I don't feel that would be very safe. I've also heard of guys using a chain as a top link to allow more float but again creates a safety issue.