You raised an issue that securities tokens are nowhere to trade yet.
There has been recently an ICO which sort of went under radar of majority ICO youtubers and various ICO spreadsheets. GBX is a new blockchain-based exchange launching in April 2018 in Gibraltar https://gbx.gi/. They plan to trade cryptocurrencies-fiat, tokenized securities as well run ICO. Their ICO was very well organized and ran smoothly.
Their ambition is to become a leader in tokenized securities. Gibraltar’s government has adopted in 2018 new legislation which completely covers this venture from legal point of view. This is definitely a project to keep an eye on. They plan to do everything Polymath does plus the exchange itself. And the GBX team and their partners dont look like a joke at all.