If you have an UPPAbaby VISTA from 2014-earlier, your stroller is compatible with the UPPAbaby MESA car seat using an adapter. The adapter is not sold by retailers can be purchased directly from UPPAbaby.
Other car seat adapters for the 2014-earlier VISTA are sold out and have been discontinued by UPPAbaby.
If you own an UPPAbaby VISTA from 2015 or later, no adapters are needed for attaching the UPPAbaby MESA your stroller. Car seats from several other brands are also compatible using an adapter. See this page for details.