Following up on a comment from Owen, I was looking through the Good relations Ontology (widely used in eCommerce sites) and noticed it has a property gr:availableAtOrFrom defined:
"This states that a particular gr:Offering is available at or from the given gr:Location (e.g. shop or branch)."
That looks pretty good to me. The range of gr:availableAtOrFrom is gr:Location which is defined as: "a point or area of interest from which a particular product or service is available, e.g. a store, a bus stop, a gas station, or a ticket booth."
The domain of gr:availableAtOrFrom is gr:Offering, the definition of which is a little convoluted: "An offering represents the public, not necessarily binding, not necessarily exclusive, announcement by a gr:BusinessEntity to provide (or seek) a certain gr:BusinessFunction for a certain gr:ProductOrService to a specified target audience. An offering is specified by the type of product or service or bundle it refers to, what business function is being offered (sales, rental, ...), and a set of commercial properties. "
To me these definitions match ours closely enough that we can just re-use them and not define physicallyAvailableAt. Using gr:availableAtOrFrom implies that a Public Service is also a gr:Offering but that doesn't seem unreasonable??