Arte Forme, Ec1 Bathrooms (20% discount) "Flow" is the simple modern style range https://arteform.co.uk/product-category/flow/
i looked there earlier but they don't do a fully exterior shower - their rainwater heads are all hidden style
Crosswater MPRO? e: not unlacquered, but they are brushed.
I may be misunderstanding what you mean by rainwater shower, but all their shower heads attach to all their arms so you can mix and match (within a range at least) so you can have external or ceiling mounted (what you are calling internal?).
@gillies started
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Arte Forme, Ec1 Bathrooms (20% discount)
"Flow" is the simple modern style range https://arteform.co.uk/product-category/flow/