As mentioned above, think aiding is like a 2% chance of getting a BP so you need to polish/motivate 50+ people to get 1 BP. Make sure you do it manually if you just hit the aid button and they have nothing to polish/motivate you wasted a chance at a BP.
Best way is to jump on to someones GB and put FP's in it. Make sure you put in enough to get a contribution reward that shows a BP as a reward. Low level GB's = less FP's to level it and get rewards but only rewards a few BP's. Higher level GB's will require a lot of FP's to level them but the rewards are greater. Scan through everyone's city and see if you can see one you can jump on and get rewards from without breaking the bank. If you have a good guild they will work with you to get you the BP's you need. You will end up with lots of duplicates before you get the full set. You can exchange 3 for 1 and keep 1 so you loose 2 BP's (swap 2 for 1 but you loose both in exchange for a random BP). Once you have the full set this allows you to level it to level 10, after this you need a complete new set. If you plan on leveling it high, 20+ for example, then only exchange until you get the initial full set or you will wish you had kept those duplicates later on.
When jumping on someones GB make sure they are still playing or it will never level. Either message them (some don't reply or can take a while to respond) or what I do is look at their tavern and see if its full. If its full they are either busy or stopped playing. If its only half full then they are active daily. (not 100% accurate but not far off).