Upgrading pyromancy flame without the two NPCs?

I'm playing as a pyromancer. After defeating Quelaag I found the egg guy under the Bell. After answering No to whether I'd be the next servant and killing him, after he wouldn't let me through, I talked to the Firekeeper behind him. After joining the Covenant I got the pyromancy of her. After some time I got back to Firelink Shrine and talked to Laurentius. He took of to Blighttown...

Now, with egg guy dead and Laurentius hollow, is there any way to upgrade my Pyromancy Flame +8 any further in this playthrough?

There is a third NPC who can upgrade your pyromancy flame besides Eingyi (the egg guy) and Laurentius. Quelana of Izalith will appear in the poison swamp in Blighttown near the Quelaag boss arena, when you have a Pyromancy Flame +10.

According to the wiki, she also appears if you host a phantom who has a +10 or higher flame in Blighttown, the Depths, the start of the New Londo Ruins or the Demon Firesage boss room. That way you can make her spawn and upgrade your flame further, because you don't have a way to do so currently. I never tried this personally and don't know if anything changed about it in the remaster.

Since you beat Quelaag already, you can't host in Blighttown anymore, but if you know someone with a +10 flame you can try it in the other areas. You can also have a phantom drop you a +10 flame to get Quelana to appear. If you don't know anyone who can help you with this, here is a place where you might find someone to trade a flame. You can also give the flame back to the owner once Quelana appears and you upgrade your own flame.

There is no other way to upgrade the flame until NG+.