Just use Yaourt. It automatically searches both the repositories and the AUR by default. It also allows you to install the AUR packages just as easily as normal packages.
To install a package you know the name of (either in AUR or repositories):
yaourt -S <package name>
To search (both name and description) for a package both in AUR and the repositories:
yaourt -Ss ANY NUMBER OF KEYWORDS
To search and interactively choose which packages to install:
yaourt KEYWORDS TO SEARCH FOR
The quickest way to install Yaourt would be to run the command:
bash <(curl aur.sh) -si package-query yaourt
This uses the aur.sh AUR helper to download Yaourt and its dependencies.
pacman -Q <package name> actually just lists programs you already have installed. I don't know why that would be a relevant answer to the question.