Here is a closer pic of the reg. It's low rez, but if you look closely where the alloy body of the regulator is and the brass piece attaches to it, it looks like that would have to be a threaded connection and you can see a little pipe dope showing.
You would need to leave the brass fitting in place on the tube above it that has the holes in as that is where the fuel and air would mix together. It's a case of just removing the alloy body of the regulator and finding a suitable valve or as someone suggested, running full on or off.
The 2nd pic shows the type of control valve you want. This is a Camco item. Looks like you might be able to modify it with the right fittings. The valve in the 3rd pic is made by Magma. I would google "LP propane gas control valve" and see what you can find. Or go to a local BBQ shop and see if they can help.
The easy part is finding a hose with quick connect fittings. This grill appears to be a bit of an oddball for doing a conversion to it. Might be easier and possibly cheaper to find say a Weber Q100 which is straightforward to modify. If you are not familiar with working with propane fittings, get a professional to do it.