Tamiya has a "Liquid Surface Primer" in 40ml jars (actually two, it comes in white or grey). It's similar to Mr Surfacer but can be cleaned up more easily as it's fully soluble in ethyl (denatured) alcohol. In a pinch it can also be thinned with ethyl alcohol for airbrushing.
However, it's a little softer than Mr Surfacer when dry.