Slowly, but surely, the Sims 3 store is making more and more of the premium content available for individual purchase. As of today, The Barrier to Entry System is available for individual purchase.
It would be a good idea to check the Premium Content section as there may be even more items you want available separately. For details on the Premium Content available in The Sims 3 Store, check out our Sims 3 Premium Content Guide.
Hat Tip: CmdrSalt