addgene.org has numerous plasmids containing IRES elements and the DNA sequence of those elements along with the sequence of the rest of the plasmid are given as well.

IRES elements are found downstream to 5'UTR of DNA's which do not contain 5' capping, you can scan for AT rich region in plasmid, AT rich regions are reported to initiate translation via IRES mediated pathway 

We use MIGR1 to introduce gene-IRES-GFP retrovirus into primary T cells and T cell lines: https://www.addgene.org/27490/