IIRC you can find the parts to make a garden hose adaptor at HD.
You'd need the copper female hose connection adaptor (IIRC it is a female garden hose connection X 1/2" FPT), and a john Guest fitting (1/2" MPT X 1/4" john Guest) to connect the RO tubing. Both parts should be in the same section of the same isle in HD, right by all the tubing, next isle down from the PVC pipe and parts.