Could be synchro's on 1st & second [like a pair of phosphor bronze gears that run together between the main gears to slow everything down to allow it to engage - when you're rolling the gears will be moving so have a better chance of meshing them.], if so it's a gearbox rebuild or replacement [usually service exchange best option].
Might find that one day you just can't get 1st & 2nd at all.
Have you tried accelerating gently, de-clutching, applying gentle pressure into the gears and slipping the clutch out? Might be able to engage 1st that way?