Hard to say without seeing it - but that definitely doesn't sound like a clutch issue - or you wouldn't have the other gears.
Sounds more like either the shift cable is messed up, not allowing the shifter to move far enough to actuate the shifter arms on the transaxle. Simple as needing an adjustment, new cable, made need new cable bushings, or similar. Sometimes, something can physically block the shifter arms on the outside of the transaxles from moving correctly, usually shows up as either the top row of bottom row of gears non-selectable - just like in your case.
Does the shifter get kicked out of gear or just doesn't engage it properly? Does the shifter bind or stick in any of the shifter positions? Unusual noise when shifting? Try it with the car off, windows rolled down - see if you can hear the metallic clanging of the shifter cables moving the shift levers on the outside of the transaxle.
Could also be something more serious - could be a broken or loose shifter fork(s). I think they are held in place with a ball and spring - if that falls out, the fork will not move as intended. That could be a lot more expensive than a clutch job - looking at rebuilding the transaxle at that point. Another possibility are the synchros are cooked in those gears - might try double clutching and see if the gear will engage.