Pretty much any transmission from a 105 or 115 Alfa will fit your '69. Does the '69 have the "push down" -style reverse lock-out? Later boxes had a simpler system, which I feel is better (doesn't rattle like the "push down"). Later boxes also relocated the switch for the back-up light, which may necessitate making simple extensions to the wiring. But again, that change represents an improvement; the BU light switches on the earlier transmissions are inside the bellhousing and as such difficult to access.
My point is that you don't need to locate a 1969 Sprint transmission. One from a '76 spider (say) will fit as well.