You might try the rpm option --nodeps
; that should cause rpm to ignore missing dependencies. You are then on the hook for installing them yourself. /bin/bash and /bin/sh should already be in place (although on Ubuntu /bin/sh pointing to dash might cause problems). If you've already got rpm installed then I think you can ignore rpm-build:
$ rpm-build
No command 'rpm-build' found, did you mean:
Command 'rpmbuild' from package 'rpm' (universe)
rpm-build: command not found
No guess what textutils covers. You might try grabbing that package from a centos repo, and unpacking it. (Google how to do it but has something to do with cpio and a pipe.) I suspect that those files might be part of your Ubnuntu install already.
Good luck but proceed with extreme caution. As others have noted mixing rpms into an otherwise Ubuntu system may cause problems.