Hello. For ISSR you don´t need a software, I think. In articles already published, there is usually a whole set of primers you can try. UBC primers, for example, are well-known. You just choose some and order the sequences in the company you prefer.
I perfectly agree with Julia. For instance, there are long list of UBC-primers and you will choose those primers that works well for your template DNA and PCR reaction conditions. the primers can be di-, tri-, tetra- or pentanucleotide.