Tasca catalog is great for finding OE part numbers, and great for getting good prices as long as you’re never in a hurry.
Their stock is totally hit and miss. I usually email and ask to check stock first because often if you blindly place an order, you won’t get an email until several days later about an item being back ordered.
That’s also the case with a lot of the online OE parts dealers. Some have better stock listings than others (especially if they show quantity).
More often than not, if I need something quickly, I go to eBay once I know the part number and find the listings from the actual ford dealers that sell on eBay. They typically always show the exact quantity they have in stock due to the listing requirements and usually ship more quickly