There are a few options available. First is just get large and small flying bases and call it a day since the models themselves are just there to look pretty and all measurements are from the stem and base.
The second is to brave ebay and slowly acquire a few things. For IN and Chaos you don't need a whole lot, maybe one battleship, 5 swords, and 6 plastic cruisers. For chaos, one desolator and 6 plastic cruisers.
The last is to use models from other manufacturers as proxies or seek out some of the fan proxies if they are available.