Some things to try to help make a diagnosis:
1. Try double clutching. In days before synchros this was the meathod used to shift gears. This will rule in or out the synchros.
2. If the synchros seem OK, try to shift without using the clutch. I used to drive a truck and learned this technique. The cluch was only used for 1st and reverse. I've used this technique in my Mustang and i know it works. Start off in 1st and when you would normally shift, just take your foot off of the gas and at the same time gently pull the shifter to the 2nd gear position. Don't ram it into gear, just lightly pull back on the shifter. When the engine RPM's match the 2nd gear tranny RPM's, the shfter will pop into 2nd. Hit the gas and repeat for 3rd and 4th. If this works, your clutch is out of adjustment or AFU'd.
3. If neither one of these work, your shifter is out of adjustment or your tranny internals are probably messed up. ie bent forks