This generally isn't possible, I'm afraid. For limited duration testing / PoC, Meraki offer free trials, which can be claimed into a separate Dashboard Organization. Bear in mind that some architectures pretty much require a common Organization to be used: i.e. if you wanted a test SD-WAN branch, you'd really need it to be in the same Org as the Hub MXs to which the branch MX would inter-connect.
For Cisco partners, purchase of similar equipment can be done on a Not for Resale basis, with appropriate discounts.