Where can I buy an Insevio stroller frame?
Unfortunately, just the chassis, probably nowhere, at least just so. The only way to get your hands on a frame only is usually to contact either a direct distributor or seller of the Insevio stroller brand around you, and ask for the frame only as a spare part... or to contact Insecio directly (email@example.com) and ask for the availability of a frame.
Watch out as it can be impossible, or difficult, or quite costly, taking the part & shipping cost into account. Some mums get their parts, even a frame, by buying the whole, used stroller second-hand and use it for parts they need, just to save money... So that could also work for you.
I wish you good luck, stay safe!