I use the rodipet hybrid mix alpacassei mentioned for my robo and it's great. Better than the Bunny mix imo. But with 5 of them the price would be really high. Have a look at mixerama (probably
this one) or the
getzoo mix as both come in larger quantities and work out cheaper despite the high postage cost. Good quality & high variety balanced mixes, much better than the ones you'll find in this country.