There's two possibilities when there's a relative clause following a list of nouns. The same applies to a bare "-ed" adjective, like:
imported computers, machinery and furniture...
1) The meaning is ambiguous.
In your example (and my version with just "imported"), it is impossible to know whether "which are imported" applies to "computers" or the whole list. It's grammatically correct, but is a low quality sentence because it's unclear.
2) The meaning is semantically indicated in the context.
At the market, I bought a hockey stick, a rechargeable razor, and a bicycle which had flat tires.
Here, "which had flat tires" clearly refers only to "a bicycle" because hockey sticks and rechargeable razors cannot have flat tires.
On my way to the wedding, I picked up my mother, my sister, and my book of poetry, which I've always found inspiring.
Here, my mother, my sister and the book of poetry could all be found inspiring, but the pronoun "which" can only refer to a thing, not a person, so we know that it applies only to the book of poetry.
Machinery, furniture and computers which are imported are more expensive than ones made locally.
Here, the context of comparing imported items with local items makes it clear that "which are imported" applies to the whole list.