"In my 3rd party software tool, using gbXML, I can only import 50 spaces at once. I wonder if it is possible to select the number of space or even the spaces itself for export process?"
Likely, the easiest way to deal with this is to (ab)use the Phases feature of Revit. When you export gbXML, you have the option of which phase you are analyzing. Since spaces exist only in the phase they are created, you can use this to control which spaces are exported.
For example, starting with a floor plan view configured for the Phase New Construction, you can create new phases and spaces for analysis.
From the Manage tab of the ribbon, Phasing panel, click Phases, then define however many new phases you will need… in this case, I am just creating two new phases.
Then, rename the views appropriately, and set the Phase property of the view accordingly.
Back in the original view, select the Spaces you want for a particular phase, and select Copy to Clipboard.
Next, open the appropriate phase specific view, and select Paste > Aligned to Same Place
Now, when you export to gbXML, you can select the specific phase (and thus spaces) you want to analyze.