Is the relevant sense that of "get existing or create"? For example, someone who would search the stores for you for a part, and if not present would machine one up for you? You could use something like provide, order, prepare, or requisition.
On the other hand, if the emphasis is upon you actively getting or creating the part for yourself, I'm not sure there is a specific word for it. Perhaps produce, because that has a general sense of bringing something forth, either by finding and showing something already possessed, or by making.
A third sense, which is more adminstrative in nature, is where you are either getting a copy of some existing information, or generating the information and then taking away a copy of it - but in either case, there is some sort of master list or cache being maintained. This differs from the upsert in that there is no updating of existing information if it already exists, and the emphasis is more on what is retrieved in either case (perhaps an identifier, or a voucher, or similar). You could possibly use words like register, audit, affirm, attest, or book out. I think none of these words quite meet the sense head-on though.
If the emphasis is strongest on the "getting", rather than on the "checking and creating", I might fall back on produce again. If the emphasis is on the "checking and creating", I'd probably plump for attest.
For example, a method which gets a birth certificate from details submitted, would be "ProduceBirthCertificate", or "AttestBirth", depending on whether the emphasis is on what is taken away, or what is being given and checked (potentially not for the first time).