Joomla and Virtuemart Expert required

We are having an e-commerce website and are currently installing further modules and extensions.

We need someone who has extensiv knowledge in Joomla & Virtuemart and can also fix any bugs and errors.

We need someone urgently. The work is not everyday but time to time, we require someone and just to keep an eye on the website.
It's more like a technical support role and needed when required.

We are prepared to pay on a monthly basis for this.