It appears you'll have to register .uk.com elsewhere.
It's not listed on dreamhost's pricelist https://www.dreamhost.com/domains/pricing/
Which means they don't have a reseller agreement. I don't think .uk.com has a local presence requirement, but it may have restrictions.
The good news is registration and hosting are two different things. You can register the domain elsewhere and host it at dreamhost. The simple way to achieve that is to set the domains name servers to ns1.dreamhost.com, ns2.dreamhost.com, ns3.dreamhost.com. Those setting are made at the registrar's website after you register the name.