Junior props
Apart from hazelton there is no stock
If you just mean close to NRL ready props the top 30 currently has BHU (28), Rudolf (27), Hunt (28), Williams (27), Kaufusi (24), Hazelton (24), Colquhoun (22) and Finucane (32) (if needed) so volume is not a problem, nor is danger of them all aging out anytime soon.
Swapping any of them just to have someone younger risks a Kaufusi scenario.
Bulldogs middles 'coming through' are who? Patolo (22) and Hughes (22)?
Tigers middles coming through, Seyfarth (24), Pole (21), Matamua (20) and S Fainu (22)?
So Tigers do have quite a few young props in their top 30 - I'd swap none of the Bulldogs or Tigers guys mentioned there for Hazelton or Colquhoun though. Pole the closest.