You want your counters to be free and versatile, and unlike An Offer You Cant Refuse, Swan Song, Force of Negation, Flusterstorm, Dispel, and Spell Pierce, this can counter creatures
In my years of personal experience, examining good decklists, and talking to people much smarter than me, 50 mana sources is about the right number for most decks to shoot for, usually 37 lands and 13 ramp sources for a general budget deck
Tsapko's RW deck played ten such finders
Cards are ordered according to their TCGPlayer Market Price, which you might pay on average for a copy of the (first edition, where applicable) cards below
The persistence and value he brings give him a significant degree of inevitability which is nice
That was thanks to a licensing deal with Magic the Gathering publisher Wizards of the Coast