Convert seed based measurements to pre-ground?
Converting whole spices to ground spices is not as simple as matching up the weights. Ground spices have a distinctly different flavour from the whole. The freshness of the grind will also affect the taste quite considerably as well as how carefully they have been stored. When the spice is freshly ground it will have a very strong intense flavour, so you would reduce the amount you use slightly. However, ground spices rapidly loose parts of their flavour. The taste changes and you may find you will end up using more than the recipe states in order to get a similar taste. However, you'll never get exactly the same taste, grinding changes the spice.

The best solution is to try to get an supply of the whole spice from an online store. You can then use them whole or grind them yourself, fresh, as the need arises.