Updated 15 May 2017 – Thanks to M.E. for their input.
There are quite a few options in the area for horse riding lessons. I have compiled this list from fellow readers, but I have not used their services myself. I hope this helps you find a location that works for you.
Zum Wasserwerk 3, 52538 Gangelt-Niederbusch
Instructors speak English. The rider can be registered in Germany at their riding level.
Tunnelweg 1 Landgraaf, Netherlands
Lessons are given in Dutch and English. Prices are at the bottom of the website.
Michiels van Kessenichstraat 75, Limbricht, Netherlands
Manege Ten Eijsden
Ten Eysden 1, Geleen, Netherlands
Douvenderweg 27-A, Oirsbeek, Netherlands
I couldn’t find a website, but here’s a link to their Facebook page.