I'm using a PC running Windows 10 which unfortunately has only one VGA and no HDMI outputs. I recently went down to my nearest generic electronics store and asked them how I could split it across two monitors. They sold me a VGA splitter. Now I've got it setup it's displaying duplicates OK but when I went to setup continuous screen in display settings it can't detect the second monitor. Is there any way I can maybe setup a virtual monitor or something so I can use continuous screen with the second monitor, which is physically there, but it can't detect?
A VGA splitter creates a second connection to a monitor, but only for the purpose of duplicating the original image. This would be useful if your second "monitor" was a projector that required VGA input, but is not useful for your objective.
If your computer has a set of PCI-e slots, you can purchase an additional graphics adapter compatible with Windows 10. You also have an option to use a USB-HDMI adapter if your second monitor has an HDMI input.
If your computer has a currently installed graphics adapter and also has an on-board video output, you can re-enable the on-board video to provide for the objective you seek. This is not as likely in today's systems.
If there is no option for adding internal components to your PC, you will want something along the lines of the now out-of-production Matrox DualHead2Go or TripleHead2Go adapters that will take two roughly identical compatible monitors and connect them to a single port on your computer. The box does the 2-to-1 conversion for you and you get a single, multi-monitor spanning desktop. The box does not take the monitor bezels into account.
It will be a single desktop though, so by default, maximizing a window will cause it to span both monitors. It originally shipped with some software to fix this but I doubt that it's Windows 10 compatible. Fortunately windows 10 has a built in feature where dragging a window to the left or right side of your screen will arrange it side-by-side.
There are some available on ebay I'm sure.
If you go this route, make sure you get one that connects to VGA and whatever your monitor's have. There are various input & output combinations of VGA, DVI and DisplayPort out there.
Its also worth noting the specs of your monitor. They will need to support the resolutions and refresh rates available.