These shapes from Learning Resources are a great alternative to the rather costly Montessori Constructive Triangles. They don’t have all the same shapes but they have other ones (circles and 1/2 and 1/4 circles) and enough shapes that I think the few missing ones aren’t a big deal. You could make them yourself with laminated paper or cut them from heavy plastic of some sort. The quality is great (nice and thick) and they don’t have sharp edges
These have the added bonus of being able to use them with a light table and they can be used as a sort of tanagram to make pictures with. Tanagrams have been shown to improve a chid’s math thinking.
The set can be purchased at amazon.ca