a lot of companies (that sell their own products to the customers themselves, as opposed to a 3rd party site like AmericanMuscle) will still make discontinued products per request, you just have to email them or call them and tell them you are interested in a discontinued product. as long as they still have the materials to build whatever it is you want, then they will usually make it for you.
for example, i emailed ABCexclusive because i was interested in just the abc lip part for the cobra bumper, and they told me it wasnt a stocked item anymore due to that they stopped producing them. they did however tell me that if i was interested, they would make it per special request.
it may cost you more to have it built as opposed to when they used to "sell" the kit, but it may be cheaper than having to do a PI swap to make the 99-04 kit fit.