Lost landcallers

How do I get to 390 so I can do LFR without doing mythic+?
I'm sitting at ilvl 383, I have my Lost Landcaller set (mostly 385) + 2 piece Drakebreaker (upgraded to 385) . I would like to get into LFR this weekend, but apparently I need to be 390. Been farming rares in a raid in the new cavern the last few nights and got a 402 cloak after 2 dozen rares...but I'm going to need more than that. I am almost maxed out on flight stones, and I'm not sure what to do with these. Can they buy gear that is 400+ ilvl?
I'm a Balance Druid, if that helps.
What do you folks suggest I do to get 390 as quick as possible? Thanks!
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EDIT to add: I have 9 Crests and am now maxed out on flightstones (2000). I did keep some 380ish greens that look like they can be upgraded...I am lost on what to do here, so any advice is appreciated.

I went to upgrade my M+ pants, got the prompt “are you sure you want to upgrade [your M+ pants]?” I hover over shoulders to check that I don’t want those instead. I decide nah I want the pants, so I hit okay on pants.
You have received Lost Landcaller’s Mantle

Edit (2/2/2023): Since this post seems to get a lot of traffic from searches I wanted to add / change things to help new readers
An overview of the Revival Catalyst
TLDR on Catalyst charges: Once the catalyst is unlocked you get an account wide weekly quest (any character at max level contributes to the completion) that gives you a single catalyst charge (to a max of 6 charges) for all characters (current and future) on that account which each character individually uses.
Example: You complete the weekly quest 3 times for a total of 3 charges. If you used 2 charges only on your main character any other character you have will still have 3 charges. Also, getting a character to level 70 afterwards will give that character 3 catalyst charges to use.
Now, with the Revival Catalyst out I wanted to hopefully help others make an informed decision on what piece of armor to upgrade for PVP. A few things of note regarding the Catalysts interaction in PVP...

• Epic world PvP armor and Crimson Gladiator PvP armor can be converted to tier set pieces (honor bought PvP and crafted PvP armor cannot be converted) and will keep their respective PvP iLevel bonuses when in PvP.
  • Example: Crimson Gladiator gear scales to 424 in PvP, so once it's converted to a Tier set piece it will still do that
  • You can also still upgrade the PvE item level of Crimson Gladiator gear with Honor once converted to Tier
• All items converted to Tier will have the "Normal" raid color look for transmog purposes
• Whatever gear you upgrade to tier in the Catalyst has set stats no matter what you put in
  • Example: These Gladiator Gloves will turn into these Tier Gloves but with the 424 PvP iLevel boost

So you can see what stats will be on your tier sets... here are links to help you check and choose which pieces you'd want based on what stats are important to your spec.
Warrior
Paladin
Death Knight
Evoker
Hunter
Shaman
Rogue
Demon Hunter
Druid
Monk
Warlock
Priest
Mage
Happy converting.