Those removable hard tops are not OEM, but are aftermarket tops. Do you know the name of the company that makes it? It might be difficult to find support arms that were manufactured specifically for that top, but normally they are just basic hydraulic lift supports. You may be able to find something that fits by carefully measuring the height that you need, and searching the internet for hydraulic lift arms……
Since you apparently don't have the original struts, use the ones you bought as a guide to determine the size you need as BEX suggested. These lifts/supports/struts are available in a million different sizes. You just need to find one that matches your need. Don't just look at the length -- look at the connections at BOTH ends!
For example, I wanted to put struts under the HOOD of my Tracker -- to hold it up instead of the support bar. Much to my surprise, I discovered that the supports from a 1976 Honda Civic HATCHBACK are a perfect match for my 1991 Geo Tracker HOOD project. Who would have thunk?!?!?!?!?
Is it the complete strut that is missing (leaving just bolt/screw holes on the hard top and rear window - or are the struts missing and the strut mounting brackets (they will typically have a little ball on them still there?
Maybe pictures of the window and the frame of the hard top would help us help you identify what's missing.
If the mount brackets are there, what you need to do is measure "center-to-center" the open & closed lengths and then get a strut that has a closed length a little less than your closed length, and an open length a little less than your open length.
If the brackets are missing, then finding replacements might be a challenge, depending on what the mounting surfaces look like - generic brackets are available (try Amazon), but you might need to drill new holes.