If you mean Belgians for 1914, purchase any suitable model of a German Model 96 77mm gun ( any number of companies make these) and replace the shield with a curved bit of plasticard or better still buy the Woodbine Design Turkish version, they've done that bit for you, it was essentially the same gun. Landships should have plenty of photos as guidance. Crews would have to be converted. Not sure off hand what Belgian artillery crews looked like in 1914 but I suspect a head swap would probably be about as much conversion as would be needed.
Post 1915/16 just use French guns and crews.