Real talk here but asking for an equivalent to REMA ammo isn't that much of an upgrade to what is currently available partly because ninjas already have access to rarer higher dmg shurikens but not in easily obtainable quantities to use with sange and wouldn't increase dps that much since the actual dmg from throwing is only a small portion of a nins dps


For example the best physical bullet you can easily get in quantities is Achiyal. Bullet at 253 dmg 20 racc/ratt. Compare to say eradicating at 289 dmg and 30 racc/ratt. Difference between the 2 assuming using annihilator is about 9% increase in shooting base dmg and depends on ws but maybe 5% increase in base dmg to ws and of course the extra 10 racc/ratt

Now the best throwing dps shuriken you can get in quantities to sange is gunna probably be Sasuke Shuriken and even that might be iffy given the price at 99 base dmg 3 agi and otherwise the same. While Togakushi shuriken is 104 dmg 3 agi 5 acc/att and 10 racc. So already available we have something that increases our throwing dmg almost as much as the rem bullets helped shooting dmg base dmg and arguably helps even more with acc since it helps the nins melee too. Giving something with slightly higher than Togakushi wouldn't be game breaking... especially since most your melee this and all your ws dmg is with the katana. Giving us a rem dispensable shuriken with similar increase of stats over the common shuriken to what rem bullets had over common ammo would result in rather small increase in overall dps but what it would mostly do is enable the usage of sange without spending a ridiculous amount of time farming or spending gil or using lower ilvl ones that will be more prone to missing