SSL cert provider with SHA1RSA still supported

We have recently updated our SSL cert.

It all goes well, except for one client. They're using their own custom software to connect to our webservice.

Problem is their software is not supporting our current SSL cert that have SHA256RSA signature algorithm. They support SHA1RSA only currently. (They schedule to update it in few months).

We have tried few options. But none working so far.

So we're back to the SSL cert. We're thinking of creating custom subdomain for this client and purchase new ssl cert that have SHA1RSA signature algorithm.

We have contacted our vendor but they cannot provide SHA1RSA cert anymore.

So, guys do you know any ssl provider that I could go and buy SHA1RSA cert?