The solutions I can think of are:
- Auto-complete
- Recent associations
- Smart associations
There may be more depending on exactly what you're doing, so feel free to add more details or screenshots and I'll think on it more.
Auto-complete
Using an auto-complete field would speed up the process for your users since they wouldn't have to hunt through the table for the association. Rather they could just start typing and have a suggest box appear below the field that allowed them to select what they're looking for.
If you matched your auto-complete on several key fields (i.e. manufacturer and product name), there's a pretty good chance that the user would be able to find the association quickly.
You could also code the suggestion box in such a way that it showed multiple pieces of key data. That way if the user wasn't quite sure what they were looking for, typing a few characters in the field would give them an idea of what they could search with.
Recent Associations
Below your auto-complete field, you could add the 5 to 10 most recent associations that had been made. That would allow your users to quickly add many products to the same association without having to use the auto-complete each time.
Smart Associations
Separate from the above two mechanisms, a smart association is something I first saw when theming a Shopify store. They allow you to automatically create associations based on the products key fields by defining conditions to include or exclude products:
Create Association 'Pants'
Where product title contains string 'pants' or
Where product title contains string 'capri'
The above is controlled by a set of dropdowns and textfields and got around the pain of manually creating associations.