leejmurphy

This plugin will allow you display the Domain Checker integration code for WHMCS in a nice tidy widget. You MUST have WHMCS installed in order for this plugin to work.
You can follow this plugin on <a href="https://github.com/leejmurphy/wp-whmcs-domain-checker" rel="nofollow ugc">Git Hub</a>

LJM WHMCS Domain Checker

A simple plugin for WordPress that allows you to display the Domain Checker for WHMCS in a nice tidy widget.

Nerd Warehouse

Allow users to check domain name availability directly from your website. Availability is shown without redirecting users. With the use of widgets you can add the domain search to multiple locations on your website. You can also quickly check domain availability yourself using the admin dashboard widget. This plugin is multisite compatible and free.
WordPress Domain Search is powered by <a href="http://www.nerdwarehouse.com/" title="Best WordPress Hosting" rel="nofollow ugc">NerdWarehouse.com</a>. Nerd Warehouse is a low-cost domain registrar and hosting provider that specializes in <a href="https://www.nerdwarehouse.com/products/wordpress" rel="nofollow ugc">WordPress Hosting</a>. Data centers in the United States, Europe, and the Asian-Pacific support our massive cloud hosting network and we offer localized 24/7 phone support.

WordPress Domain Search

This plugin allows you to create domain search widgets and check domain availability from the admin dashboard.

LJM WHMCS Domain Checker vs WordPress Domain Search