Most window manufactures can make and do make custom sizes within some limitations, We have, in the US, a huge variety of widow sizes even within a single project. The cost is difference is minimal as so many window manufactures are making replacement windows that need to fit into odd sized or even shaped openings when you order a window from a manufacture is is custom made per each job each opening and the cost is almost the same as if it were bought from a store with a set size.

A nice high-end system is "vitrocsa" specifying it now for a project in Manhattan

The big 3:  Anderson, Pella, Marvin

They have varying grades of windows, massive distribution networks and have been around for decades.

Jeld-wen may be at the top of the list per a lunch and learn last week.  They are also really big in doors.

Yes Lior google is the best guy you can ask. To make your search more easy horizontal sliding windows are called double hung windows. At my firm in Princeton New Jersey we like the following window manufactures Anderson, Pella, Jeld-Wen, Velux and Kurpiewski Window Manufacture. All make great double hung windows and skylights. I personally only use Anderson A and E series window when a wood finish is needed. When a wood finish is not required i only use Kurpiewski Window Manufacture since they only manufacture vinyl windows. Hope this helps you Lior Cheers old friend.