For some free options:
Critical path analysis is also taught in business studied I believe, so that can be a source for questions.
Kruskal's/Prim's algorithm questions can be found by just googling a random worksheet on them. (Or you could also just google up random graphs and apply Kruskal's/Prim's on them, but that might be a bit unpleasant due to lack of answers.)
For the shortest paths, search up problems on Dijkstra's algorithm (not the programming version, just a worksheet version) and try computing some of the shortest paths in just the way you were taught. However some questions might go well beyond the expectations of Maths Standard.
Sadly wouldn't have a clue about the flow networks stuff :/
You can try searching some problems on the Ford-Fulkerson algorithm, because that theorem is designed to help you find a maximum flow in a flow network. However much like Dijkstra's for shortest paths, I'm not too sure how useful it will be.
Otherwise, there's always the AN topic tests and various other textbooks out there.
Inevitably there's going to be fewer questions for fewer topics. As a student this is ridiculously frustrating, but nothing can be done about it. Remember that everyone else is in the same boat as you are with this issue.