If you want to know if a symbol is portfolio margin eligible, I can look it up on the OCC PM calculator. That does not mean your broker will not have an add-on for low volume. Give me a few symbols and I’ll look them up for you.
Interactive Brokers is good for this when the market is holding up. But they increased margin requirements by 2-3x during the 2020 crash so plan accordingly for your drawdowns. most other brokers don’t give much in the way of decent margin on preferred stocks.
Second MoreLeverage's comments. Prefs and baby bonds are bad to lever because: 1) they trade with retail and diverge from bonds at market bottoms and 2) brokers rug pull margin on them at bottoms. You can do it as an overlay on an otherwise unlevered portfolio if you're willing to take the drawdown but be careful. Safest money is to buy reasonable credits at 50-60% of par in the big selloffs that come every 5-10 years. People with your mindset become forced sellers at those times creating these huge bargains.