I would like to make it more convenient to access the rear panel if my computer, by connecting an extension cord with many ports (preferably 2 or 4). The problem is that I only find USB hubs (which are connected to only one port in a computer). My intention is to avoid reducing the speed, therefore, I'm looking for something that connects one port in a "hub" to one port in a rear panel. Does anyone know such a thing?
I think you are probably using the wrong terms here. You seem to want basically a USB extension, cables, but with the ends that look nice. What you may be looking for would be something like a USB patch panel.
These are mostly used for rankmount servers. I haven't really seen anything targeted at the desktop market.
I don't have an particular experience with any of these vendors or models but a google search for 'USB patch panel' gave me these hits, which may get you pointed in the direction you are trying to go.
You might also be looking for something called a USB bulkhead adapter. These are sold as components to be put behind walk plates for high end media center type setups. Where you would get a fairly standard wallbox of some sort and matching wall plates, then you can have all the wiring for your media center run inside the wall. You may find adapters that would work, and then you could easily mount them in a standard electronics project box of some type.
There are zero products of your specification. I suggest that you purchase multiple extension cables and group them together and simply use them. I don't think you will ever reach out to the rear end of your computer to check out the plugged in cable and plug it out. You can tape those cables together.
Obviously you will have additional USB 2.0 headers on your motherboard, so I'll assume you need USB 3.0 ports. A cable that is an extension and comes from the back to front is not that elegant, it'll just add clutter.
Instead, you could get a panel that plugs to your front port optical drive bay:
and a PCI-Express 3.0 card:
You'll have a total of six ports(two on the back and four on the front).
USB works as a tree-type structure so even if you have twenty ports, all bandwidth gets split to the same bus, limiting you to 5Gbps(625MB/s).
You can keep the ports you don't use open - it doesn't really affect speed if you don't use a port.