Is there an adverb for 'customised' or 'bespoke'

Solution 1:

Your best option is probably specially

2a : for a special purpose dresses made specially for the occasion

2b : in particular : SPECIFICALLY made specially for you

Thus

The items that have been specially manufactured are safely stored.

or more succinctly

Your specially-manufactured items are safely stored.

You have to be careful, because people can misuse "specially" when they mean "especially", which has a different meaning.

Another option is individually. The adjective individual has a sense

1b. Intended for one person

If two words are OK, you could go with to specification or its abbreviation "to spec". The noun specification has the sense

2a: a detailed precise presentation of something or of a plan or proposal for something

With this one you could specify whose specification(s):

The items have been manufactured to your specifications, and are safely stored.

(All quotations from Merriam-Webster).