ohhh... becoming quite complicated - Im not sure i understand what it is all about... to make sure:
you press the clutch and it works (disengages...=the revs fall down immediately?) but You cant engage the gear? and You feel some tension on the lever, and gears are "not wanting" to go in?
then its the box probably.. im having mine fixed and I had similar symptoms (apart from the main reason which was different, but this doesnt matter) now...
the 1 & 2 gear wheel bearings on the rod in the box are probably ending their life. Id think of synchro too...
If the clutch works=disengages, and if its hard to get into gear then its great possibility that (unfortunately) im right
Go to somebody who has knowlege of boxes let him try... and prob. you will need to have Your box fixed.
I wish I am wrong and it will repair itself...
cheers