Anything you find for PCI would probably be for dedicated servers, and thus would not have any 3D acceleration capabilities.
The problem with PCI (non-Express) is that the bus simply does not have the throughput and latency required to render graphics at modern resolutions with modern techniques (window compositing, OpenGL / DirectX accelerated font and canvas rendering, etc.) so anything you find for PCI is going to be so slow and so old that you will get a "software only", Microsoft Basic Graphics ("VESA") driver on Windows 10. This is not a recipe for a good experience. Direct3D and OpenGL, if they run at all, will be unusably slow on this software-only driver.
I therefore suggest you go with AGP. Pretty much the highest-end proper GPU (with 3d acceleration capabilities, DirectX 9.0c, etc.) with an AGP connector is the Nvidia 6800GT / 6800 Ultra series. This card was manufactured til 2007 or so as I recall (released in 2005?), and there are plenty of working specimens available (new or used) in the aftermarket. You will not be able to buy a brand new one direct from major vendors like Amazon though; it's simply too old.
Luckily, Nvidia released the 309 series drivers with full support for WDDM on Windows 8, and the 6800 series cards are supported. Thus you will be able to get at least a WDDM 1.0 / 1.1 driver on this card. The Windows 10 installation may tell you that you're getting the Microsoft Basic Graphics adapter, but then you can install the R309 graphics driver installer from Nvidia and it should load the Windows 8 driver on Windows 10.
AMD (nee ATI) has a similar story with contemporaneous hardware if you prefer the red team, but I'm not sure if the drivers are even available, let alone as current as the Nvidia drivers (the R309 legacy driver was released in 2015). I recall AMD declaring that they would stop supporting old cards a long time ago. They've been in a GCN-only support mode (Radeon 7000 series and later) since about 2012-2013 IIRC.
The research I've done on AMD has indicated that the last driver available for their most-recent AGP cards was released.... in 2010. A full five years older than the latest driver from Nvidia for their AGP cards! It may not even be a WDDM 1.0 driver; I don't have the hardware to even try this driver to know whether it's the XP graphics driver model or the WDDM. If it's WDDM you should be able to peel off the packaging that says "This OS isn't supported" and force-install it on Windows 10 by directly loading the .sys files, but it may be a complicated procedure, so good luck with that.
In summary I wouldn't recommend AMD because their driver support for very old hardware is not as good as Nvidia's.