They certainly have the right, you can't get parts for a model T car from Ford. It probably comes down to the reputation for customer support of the product requiring the part that determines how long they keep those people happy, in some cases companies announce the end of support for some specific product.

There is no obligation for anyone to sell to anyone. However, if the refusal is for some illegal reason, such as discrimination on grounds of race or sexual orientation of the customer, for example, then prosecution may apply.

I f I am a privately held company and I don;t want to sell you something, I don't have to sell it to you as long as the reason is not EEOC related.

Yes.