As Warren says above, you should find a solution at a good builder's merchants (as opposed to normal domestic DIY Stores) but there are also options on Amazon for injectable Epoxy fillers for brick work. We can't recommend any specifically as its not our main area of interest but it would be a good starting point.

This is not something we would have a product for unfortunately. You might find something suitable in the DIY market. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I need to repair some cracks in an internal brick wall covered in plaster and have been advised by a structural surveyor to use a flexible epoxy sealant. It's a one-off task. so small quantity required. Can anyone recommend a suitable product?