Hello. I'm looking for a small prebuilt / office computer or case with two full height PCIe expansion slots and support for a microATX motherboard, something similar to the HP RP5810 in the picture below. Most of these computers have low-profile slots, unfortunately. Yes, and the motherboard must be LGA 1155 or older. Will be grateful.
You need to understand that the HP case your'e referring to is possible for them to make since they are doing so in a volume, so bulk discounts are seen by the brnad.//company. The brand you speak of also have boards rebranded or made to spec to fill up a product segment.
If you want a full height slot for the expansion slots, you'll see you're increasing the width of the case. At that point you're looking into an matx case. You could look through this;