Lead Liaison offers the ability to use Custom Fonts in your assets (email, form, landing page etc.)
You can add a custom font in the style tab. Simply enter the URL and name of the font you would like to use.
You can click the (+) buttons to add more custom fonts.
In your email, click the Design tab.
Click Edit Page Design.
Expand the Page section.
In the Custom Fonts section add the stylesheet link and font families as shown below. Use a new entry for each font family. In the case of 'Roboto', sans-serif, the sans-serif font if the fallback font that the email client will use if it does not support the web font.
Notice in the screenshot below how the semicolon is removed from the end of the fonts.
Instructions on how to find reference URL (stylesheet link) of a web font online is available here.