CIS Subcontractor Tax Return without Payslips/Statement

You could try ringing the company he worked for yourself? Some will send the cis statements through to you direct. If you have scrutinised his bank statement and are fairly happy that there are no further cash payments and that the figures are correct you could put a note in the white section saying that he is missing cis statements. You can request a cis statement from hmrc but they will only send this through once per client and not any future years but 'this is sticking his neck above water' if the client isnt keeping accurate records as hmrc will be fine tooth combing the client the following year.

At the end of the day it is his responsibility to keep accurate records and you are only sending what he provides, but bear in mind when he gets a compliance check it will probably be you who has to deal with it, so it might be time to press upon him the importance of keeping accurate records and the penalties for not doing so.