You can find a list of negative control shRNAs that are part of the TRC library from Sigma here: https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/marketing/global/documents/mission-control-vectors-bulletin.pdf

If you need help extracting the siRNA sequence from a shRNA sequence let me know. But section A2 and B2 of this Addgene guide may be helpful for that: https://www.addgene.org/protocols/plko/

Note that the negative control shRNA SHC016 has been found to not actually be non-targeting, so don't use that one: Article Non-targeting control for MISSION® shRNA library silences SN...