Your case will be little tricky,
If you don't want spend money to replace the electronic filter. Suggest you to measure the size of the filter, Height x Width x Depth. Build a wooden box with the measurement then buy a next size down filter fit it into the wooden box. Understand?

By the way. What is wrong of the electronic filter? It seldom any thing will be wrong, it is a very simple device………it used electrical current that general a + and – electron to attract the dust as it going though, Clean it, Dry it, and Use it again…