There is commercial extension Vm2Mage from Yireo.
Migrating data from VirtueMart to Magento is part of a bigger process: A new Magento site also requires a proper theme, a revision of strategy, marketing effort, perhaps CMS-capabilities. There for we advise Vm2Mage to people who want to make real use of Magento. Vm2Mage is a flexible tool ment for Magento sitebuilders, webdesigners and webdevelopers. If you want to migrate from VirtueMart to Magento, this extension is a real time-saver!
Current version 0.10.33 (Stable)
Requirements Joomla 1.5
Joomla 1.6, 1.7 or 2.5
VirtueMart 1.1.2 or later
VirtueMart 2.0.1 or later
Magento CE 1.7 - 1.9
Magento EE 1.10 - 1.14
PHP 5.4.0 or higher (5.4, 5.5, 5.6, 7)
There is also official Magento extension Cart2Cart
Automatically migrate your products, customers, orders and other store data from VirtueMart to Magento!
Compatible with Magento: 1.1, 1.2, 1.3, 1.4, 126.96.36.199, 1.4.2, 1.5, 1.6, 1.6.1, 188.8.131.52, 1.7, 1.8, 1.8.1, 1.9, 1.9.1, 1.9.2
Because Magento 2.0 is fairly new on the market, these extensions are probably not yet compatible with it, but you can always contact extension developers and enquire about their plans to upgrade them.