Simple, hacky AppleScript to search and copy a password to the clipboard.
tell application "System Events"
set frontmostApplicationName to name of 1st process whose frontmost is true
open location "onepassword://extension/search/{query}"
set frontmost of process "1Password 7" to true
key code 48
key code 124
key code 125
key code 36
set frontmost of process frontmostApplicationName to true
end tell