Lets give this a go

code/modules/admin/admin_verbs.dm

@@ -45,6 +45,7 @@ GLOBAL_LIST_INIT(admin_verbs_admin, list(
 	/datum/admins/proc/toggleemoji,     /*toggles using emoji in ooc for everyone*/
 	/client/proc/game_panel,			/*game panel, allows to change game-mode etc*/
 	/client/proc/cmd_admin_say,			/*admin-only ooc chat*/
+	/client/proc/gsay,					/*cross-server asay*/
 	/datum/admins/proc/PlayerNotes,
 	/client/proc/cmd_mentor_say,
 	/datum/admins/proc/show_player_notes,

code/modules/admin/verbs/gsay.dm

@@ -0,0 +1,27 @@
+// GSAY
+// Like asay but global between instances!
+// *Insert changeling hivemind :g joke here*
+
+/client/proc/gsay(msg as text)
+	set name = "gsay"
+	set hidden = TRUE
+	if(!check_rights(R_ADMIN))
+		return
+
+	if(!msg)
+		return
+	msg = sanitize(copytext(msg, 1, MAX_MESSAGE_LEN))
+
+	// To whoever says "Why dont you just topic the full message with formatting"
+	// This lets us use this in other apps, like a discord bot, without HTML parsing
+	// It also removes a way to put whatever HTML we want in the chat window
+	var/built_topic = "gsay&msg=[url_encode(msg)]&usr=[url_encode(usr.ckey)]&src=[url_encode(GLOB.configuration.system.instance_id)]"
+
+	// Send to peers
+	SSinstancing.topic_all_peers(built_topic)
+	// Send to online admins
+	for(var/client/C in GLOB.admins)
+		if(R_ADMIN & C.holder.rights)
+			to_chat(C, "<span class='admin_channel'>GSAY: [usr.ckey]@[GLOB.configuration.system.instance_id]: [msg]</span>")
+
+	SSblackbox.record_feedback("tally", "admin_verb", 1, "gsay") //If you are copy-pasting this, ensure the 2nd parameter is unique to the new proc!