When we have similar mounting requirements, as they usually are never exactly same, it usually doesn't make sense to look for specialized hardware. Therefore we normally use the necessary length of M8 steel rod (you drill a hole in the, put in the bronze M8 dowel, and screw a rode into it), some metal plate (~2x6 cm), and use 2x M4 screws fixed in AP standard mounting holes to fix AP to plate (need to use screws with the biggest heads, which can be put into the holes).
We almost always use this method for R510/550 in warehouses and industrial buildings. If rod is longer than 1 m, we use M10 or M12 to make it more stable. Such mounting is very robust, we had experience APs hit by forklifts, and even then they still not dropped down. Most important that you can get needed mounting parts instantly, and very cheap - dowels, rod, some mounting plate and screws can be found in any hardware shop.