1. The Rhodesian security forces received no "NATO Forces" support after UDI. What external support they got was from South Africa or by sanction busting. The Portuguese weren't really any help before their revolution as Portugal was dirt poor (except for the G3s their colonial troops gave Rhodesia went Mozambique and Angola got their independence).
South Africa produced 7.62x39mm ammo.
The Rhodesian sanction busters were dedicated. They became masters at it.
2. The Rhodesians captured tons of COMBLOC war material from ZANU & ZAPU intercepted units, caches, and in their highly successful cross border operations (like OP DINGO & OP SNOOPY).