Actually, I found a glitch that helped get me the four parts I was missing.
The glitch: Every day, Beedle adds two new ship parts to his store. I decided I didn't want to wait and pray, so I tested something. I bought the two parts he had, left the treasure, and set the DS clock forward (or backward) one day. I went to his shop, and he had two new ship parts! Howeever, I discovered something else: the treasure was gone. So, I bought nothing, and switched the day again. This time, the treasure was there, but the ship parts were not. This led me to test another theory. I switched the day again, causing the ship parts to come back, then switched the day
by two days. The ship parts were there, but they were different.
My point: You can cause the parts to change by switching the days in your DS. Btw, the lowest you can get them for is $4,200. This is with VIP Membership (I got a lot of point days
)