Feedback buster for 3.75in sound holes

My Brook Taw is fitted with a K&K Pure Mini p/up - for open mic and solo stuff. A couple of times recently I've suffered from low end feedback when the person running the FOH isn't the most experienced of peeps. So I'd like to try a feedback buster - a plug that sits in the sound hole. 

They're nearly all for guitars with a 4.00in sound hole. My Brook has a 3.75in sound hole. Brook doesn’t do anything and couldn't point me at anyone. I've found a Maton accessory, which is stupid money, so I prefer something cheaper. 

Anyone else know where I can find something the right size? Ta! 
Comments
camf Frets: 1203
18 Nov, 2024
A very good question. This is one of the reasons I’ve ended up using soundhole pickups (Baggs M80 and Fishman Blackstack). 
BillDL Frets: 9939
18 Nov, 2024
Do you have a tub of Cadbury or Bourneville hot chocolate powder in the house?
It may not be pretty, but one of the lids might well fit neatly into the soundhole.
camf Frets: 1203
26 Nov, 2024
Man, a few years back when I was looking for one of these in the smaller size I couldn’t find one anywhere. That’s good to know. Thanks.