I haven't looked in a couple of years. I see some sources have gone up a bit, and Amazon didn't have much before, but they do now.
I liked this for the accumulator springs, I think these are what many people use with the Jmod steps;
AODE 4R70W 4R70E 4R75W 4R75E 1-2 Accumulator springs jmod | eBay
I liked this for the solenoid kit for 98-03 4R's;
https://www.amazon.com/4R70W-Transm...=2025&creative=165953&creativeASIN=B00AAVW0GQ
That mentions Borg Warner EPC brand, many other sources don't list a brand. I saw that on eBay for $20 less and got that, same seller, shopping around is smart.
The accumulator parts are not high, but getting the group is helpful;
https://www.amazon.com/dp/B017Y515Q6/ref=psdc_15724671_t3_B00AAVW0GQ
Those are maybe $2 less individually on transmissionpartsusa;
AODE 4R70W transmission servo & accumulator pistons
But some things they want too much for.
Sonnax makes a bunch of really good VB parts for most transmissions. It's easier to browse their site and see what they have for the 4R70W, the VB stuff. Try not buy overlapping kits and parts, they do have at least three upgrade choice for the main pressure regulator, a spring, spring and valve, plus another kit I thought was more involved and better;
Sonnax Hydraulic Line Pressure Booster Kits 4R70W-LB1. Here's the same kit on eBay with free shipping if you don't need $100+ from Summit;
Ford AODE 4R70W 4R75E 4R75W Transmission Line Pressure Booster Kit 4R70W-LB1 | eBay
The Sonnax o-ring kit is good to do, and there may be a couple of other items, I've usually bought their bigger kits that have more little things in them(are for rebuilds that have some internal items beside for the VB).