Lily oil is a synthetic fragrance oil (except for extremely rare situations, and even then it doesn't smell like the 'lily' most have in mind). So we aren't working with the plant energies of lily so much as we are working with the associations and correspondences of lily. It has long been associated with the sacred, especially the sacred feminine, and with holy places, churches and blessings. The fragrance of lily (usually synthetic as above) brings many associations to mind (and spirit!).
To bring similar associations to your formula, you can substitute gardenia, jasmine (one of my favorites), apple blossom or lily of the valley. You can also make your own holy oil as described in the PaganPath article
paganpath.com/study/...8-holy-oil
by combining any of the recipes, or even using parts from all of the recipes!
It is perfectly acceptable to use what you have on hand, and it will not lower the quality or authenticity. In fact, using what is available is probably the most ancient tradition of all!