I don't know where you are located, but here in Australia and because they were research or could be used that way my interest was to ISBN them. The National Library in Canberra ACT issues them (without cost) and they issued me one for each publication as it came up but after a while they gave me a block to use. Whenever I have used up the block of numbers I re-contact the National Library and they issue me with another block. It does seem strange to pay for something that National Libraries in Australia, U.S.A. and U.K. administer for free.