It would seem unlikely that all the synchros are bad. There are a lot of possible causes for this.
a.) Clutch adjustment
b.) Clutch disintegrated, and not releasing when you press the pedal
c.) Air in the hydraulic clutch circuit. Fill with new fluid & bleed.
d.) Bad clutch master or slave (check for leaks or replace)
e.) Low on trans fluid, or wrong type, replace with Honda trans fluid.
f.) Finally bad synchros, check for metal chips when you drain fluid.