Is there a wireless charger that is compatible with a 7th generation iPad?

No.

No models of iPad support wireless/inductive charging.

In order to have wireless inductive charging, a mobile devices need to be made of an inductive material, like glass, like most of thr newest iPhone models are made of, for wireless, inductive charging to work.

iPads have an aluminium-alloy back panel that simply is incompatible with any type of inductive charging.

Sorry.