Spiking speakers not designed for spikes?

Will it be simple to find the right threaded spikes for those?

In Australia it was, as the local hardware shop had all different sizes, I just took a spike with me and he found the right size 8 of them and 8 lock nuts as well. and don’t forget the tube of Liquid Nails.

This is 4 you need 2 sets, and M8 is the "t" nut thread size 
https://www.ebay.com/itm/4pcs-lot-M8-Iron-Speaker-Spikes-Hifi-Audio-AMP-Monitor-Isolation-Stand-Feet-42mm/312225878780?hash=item48b21cd2fc:g:yUEAAOSwR7Bbg7kt

Cheers George

wooden bases that I’m nervous about removing or drilling into.

Use "T" -nuts of the same thread as your spikes, and for good measure coat the outside of the "T" nut with liquid nails before you hammer them in, and you’ll be fine I’m sure.

https://images-na.ssl-images-amazon.com/images/I/81x9eKE2eAL._SX425_.jpg

https://images.homedepot-static.com/productImages/5954888a-159c-46b2-a760-a79dcc9a1c21/svn/liquid-na...

But remember, spiking a speaker into suspended floor is a no-no as the floor becomes a sound board for the bass destroying any tightness to it. They should be de-coupled not coupled on this type of floor.
Only spike a speaker into a solid cement slab floor that can't act as a sound board. 

Cheers George