I appreciate your plight, and well remember similar looking for student
placements - er - 24 years ago.

Have you considered larger institutions/organisations rather than
domestic plumbing businesses?

e.g. hospitals, large industrial premises, council maintanence
departments and the like - all of which may have their own in-house
plumbing services. You might find qualified plumbers and qualified
electricians - rather than that being one person.

It may not exactly fit the formula - but your college isn't exactly
being helpful - and the examiners will have to be realistic about the
opportunities students can find (and speaking as a former lecturer -
quite a few of the staff probably need a rocket up the bum to realise
they should be out there building up those business networks that
students depend on).

BTW - whereabouts are you based?