I think I have version 6.2.
This is no LO question. Fonts are managed by the OS. More fonts installed in OS, more fonts in LO, but note that TrueType fonts are no longer recognised by LO, you must install OpenType one.
Search the internet for “free downloadable fonts”.
… but note that TrueType fonts are no longer recognised by LO …
Hello @ajlittoz, how this? With upcoming editions? At least up to LO 6.2.3.2 on Windows 10 and on Ubuntu 18.04.2 LTS ttf fonts still work perfect.
@OP: take a look at Google fonts. You may find some fitting ones there and you could download and install them on your system. Be aware that most font sites don’t offer fonts for free use.
I know that “PS Type 1” fonts are no longer supported, but that this should be true for “True Type” fonts also, is a quite new information.
@ajlittoz I think you are confusing OpenType fonts (which are supported by LibO) with PostScript or Type 1 fonts, which support was dropped a couple of years ago.
I had trouble not so recently with Nimbus Roman No. 9L (which I liked a lot) and tried to replace it with an .otf font. I must admit I’m not sure whether Nimbus … is a type 1 ot true type font. Nevertheless, the converted OTF looks ugly (notably bold displaying like “shadow” at small size) compared to original design and, in the end, I substituted TeX Gyre Termes family.
I apologise if I created confusion. Anyway, present trend seems to be in favor of OTF over TTF, which I regret because TTF uses cubic splines to interpolate shapes while OTF uses quadratic curves only. Though this may seem subtle, some letters are affected and differences are clearly visible.
@ajlittoz Nimbus Roman No 9 L is a Type 1 font indeed. For a good OpenType alternative, TeX Gyre Termes is directly derived from URW Nimbus Roman No 9. And sorry, but you got the splines thing the other way round 
It’s true that many OpenType fonts use quadratic splines, but the OpenType format support both, the quadratic and the cubic splines while TrueType only support the quadratic ones.
@RGB-es: thanks for refreshing my memory. I checked the converted Nimbus Roman … with the fontforge utility and it told me it had only quadratic interpolation. Then it should have been a ttf one. Shame that there is no longer any official release of this font. Anyway, I am satisfied with the TeX Gyre collection which has also solved a “compatibility” problem between serif and fixed-sized font. TeX Gyre Cursor has an x-size and a line spacing which match much better those of Termes (instead ot the various Free Mono or Liberation Mono), so that I could remove the 80% scaling from my character styles, allowing to freely mix them in body test or notes.
FYI - out of the 192 OpenType font files distributed with LO 6.2.4.2
- 8 use Postscript Outlines
- 184 use TrueType Outlines
As already commented by others, this is an Operative System issue, so you need to check your system documentation on how to install new fonts. To find free fonts, you can check the Font Library Project. Also, in my personal blog I regularly publish reviews of Open Source fonts, commenting their OpenType features and main characteristics.