Thank you for giving Andre the names of suppliers of Pot Bromide, living in England I don't know the US suppliers.
Try only one ar any combination until you get the result you want. Many problems in photography are sorted by using combinations of little dodges such as the exposure and development one and the Pot Brom one.Another dodge that I use to increase contrast is to add Benzotriazole to my developer to help increase contrast but it also cools down the print colour.
You need to make a 10% solution of Pot Bromide by mixing 10gr bromide to 100ml water, whilst not a true 10% sol'n it is near enough and if you always mix these proportions you are being consistent and will get repeatable results. Add 10 to 15 ml of this sol'n to any developer but be careful not to overdo it for you will run the risk of getting a green caste on your print and could induce a huge loss of contrast. My suggestion is to start by making a print with no added bromide and then add 10ml and make a 2nd print and then add another 5ml, make a 3rd print and so on. Eventually you will get a green cast and flatten the contrast but it is a good way to learn how far to go with these things and you will see how much bromide to add to give you the result that you like. I see you said you needed all the contrast you can get because the negs are thin, have you made prints on grade 5, if not try. Also, you may want to try adding lith developer to your normal print developer, it will certainly increase the contrast. Lith dev comes in two solutions, one of them with sodium hydroxide in it, usually the B developer, and it is this one that you add, say 50ml as a starter.