DNA construction:
You need a custom DNA sequence? You send me the sequence you want and preferably a template DNA (if the sequence is over 250bp), and I use PCR to create or edit an existing sequence, and I clone it into an expression vector of your choice (which you may have to provide if I don't have access to it). I would even consider generating viral particles carrying the DNA, but there are legal/ethical limitations as to the tropism of said virus.