To get the facts right: You, quickstart, have an injury of the peroneus Brevis/ Longus. You started to get problems during the build up after an hallus valgus Op. The Gastrocnemius/Soleus are hypertone [antagonists of the Peronei] and no further hypertone or hypotone muscles of the leg or lower back. Your running shoes are about 6 month old but not hard worn. and you are back to running 30 minutes a day.
The primary possible causes of injury:
-Overuse by too fast progression, the injury [operation of hallus valgus] needs to settle and adjust with time to the new situation. You have been a runner so you know how fast and how long you could run and that tends to make people to become over enthusiatic [at least I have that tendency].
-Gastrocnemius is hypertone, why?, Any back problems level L4/S1? Since peroneus tend to become weaker with immobilisation and the length of the Gastrocnemius shorter, it changes the balance between Peronei and Gastrocnemius and therefor easely overuse/abuse of peronei.
I think you should take it slower in your build up, have someone check up on your walking/ running to illiminate foot problems causing you problems. Get good advice on new running shoes because 6 months using a pair of shoes might cause you problems. If you have stuck to a certain brand of shoes you used before the op. that might cause the problem since the allignment within the foot has changed due to the op and therefor you need different shoes [or even inlays]
Start to strengthen the peronei, that will effect the rest tone of the Gastrocnemius [a stretch of Gastrocnemius will have a good effect aswell]. Why not use PNF paterns to do so [ you might even cause a nerve mobilization ala Butler].
Mobilizing of the bony structures within the foot might be beneficial [being in plaster doesn,t help proper movements within articulations]
And if nothing seems to help be shure your lower back/SI is playing up but this should become evident within the analysis of your walking /running as well. I assume that in Australia sport shops do have a hamster belt and they do make videos otherwise go to a sportcentre and do the hamster thing on one of their belts.
Cheers