Usually spelt Charpai - according to Wikipedia "also called a Manjaa or Manji and in Sindhi and Saraiki it is also called a Khatt, Khaatt or Khattra"

Check the web/Internet for those spellings, quite a few available on line.

Also these are apparently used across the whole of the Indian sub-continent, so do not restrict your search to just Pakistani sources.

Try either Soho Road or Small Heath - both have Asian furniture stores