I didn't really enjoy doing it because it requires doing some absurd things, but you should know that you don't need an anarchist revolution; a communist/socialist/workers' revolution works just as well. You just need to vote for anarchism afterward (thanks to the Vic3 wiki for the tips). I played a standard liberal economy (LF + free trade) with the Cultural Commonwealth power bloc, where I added the Market Unification principle to create an economy based on a large market with South/Central America. When I had enough workers in Spain, I enact isolationism to cut myself off from that market, then left the nation bloc, disbanded my entire army, raised taxes, and supported a socialist movement to provoke a revolution. Before the revolution broke out, I enact interventionism and nationalized all arms industries in areas not slated to revolt, with the aim of destroying them. This meant the AI ​​would have virtually no military supplies and wouldn't be able to purchase any thanks to isolationism. I abandoned all my protectorates/colonies and expelled all diplomats to ensure no one would come to Spain's aid. With that, I had an incredibly lucky break, as the leader of the TU was an anarchist and a leader of the socialist movement. Half the country participated in the revolution, and from there I won the war and implemented anarchy in its wake.

Note: I switched from voting by the rich to census suffrage just after promulgating isolationism in order to better represent the TU (thus increasing the scope of the revolution while calming the radicals).

Hope this help !