Almost all reagent test companies sell a selection of the same 10 or so reagents. Ketamine does react with liebermann and mandelin so you would want one of those to prove that ketamine is present at all. You then want marquis or froehde or similar to screen for adulterants. The latter two do not react with ketamine so if you see a colour change then you know there is more than just ketamine present.
My favourites are froehde and liebermann because they tend to have very good shelf lives but really any test is 10000x better than no test.
Making your own is almost never worth it unless you are expecting to test hundreds of samples per year.