kombu

Thank you!

It won't taste the same. But Rather than just bonito I'd go with the Nori...or wakiame.
For next time---have a bottle of Dashi Crystals for instant broth option; the Dashi Crystals are actually a very good sub for fresh.
Another reason for the Kombu is that it's a natural source of MSG...so if you a bit "Accent" seasoning.
And for probably the best option is use mushrooms. Boil hard...then add Bonito off heat..boil 30 seconds and strain.