I'm currently working on code that provides Views integration for Ubercart Attributes:

http://www.ubercart.org/contrib/3960

The code includes some Stock integration (i.e. you can choose to display only those products that are in stock). Including a stock level field as part of that code wouldn't be difficult. This would provide you the ability to make a view that showed the stock level of a product with a specific set of attribute options. The specific set of options could be chosen by an option select box in the Views edit page, and the default would be to show the stock level for a product with no attributes or attribute options.

Admittedly, this doesn't get the Stock level built into Ubercart's catalog feature, but if you're comfortable using Views, this should do exactly what you want.

I suspect I won't be able to work on this feature until sometime next week, but let me know if this is what you're looking for and I'll make sure to put it on my To-Do list.