Low FODMAPs Stock
Finding stock that is onion free can be a real challenge.
If you are in Australia then it is very easy. Sue Shepherd makes a stock but if you are looking for a cheaper alternative then I love Massel's 7's Stock Cubes Chicken Style. Only this type i.e. 7's and Chicken flavoured are low FODMAP but they are fantastic. They are also vegetarian, lactose free, kosher and halal.
If you are not in Australia then you are sadly going to have to make your own. I really like this version from Cook Low Fodmap, as it makes a powder that you can store, rather than having to fill your freezer with litres and litres of stock!