Logitech non-unifying receivers compatibility (and ways to get a spare)

I have bought an MK235 keyboard-mouse set and a M220 mouse which I use for different computers. Recently I lost the receiver of the MK235 set, but, doing some testing and the Logitech app, I have found that the M220 receiver is also compatible.

Both of these receivers are P/N C-U0010. After searching a bit in ebay, it seems that this specific P/N is used for variety of products, while it seems that some mouses and keyboards are also compatible with other non-unifying receivers. I have an older one (C-U0003) but it is not compatible, but this does not seem to be the rule. As expected, I have found nothing from official sources. The questions are:

1. Is there any compatibility list for devices and receivers?
2. The standard cost of such a receiver in ebay is 10+ euros. I can get a mouse with the same receiver for a similar price. Is there an official Logitech e-shop to get one at a normal price?
3. Has anyone the wireless mouse B170 or M170 to tell me the P/N of the receiver that comes with the product?

Thanks

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