The Farksolia/Farksoo folder in the Columbia University archives is very full but there are unfortunately important pages missing. Also, the archives do not include the card catalog entries of Farksoo>English and English>Farksoo words that Barbara describes in her correspondence.
Barbara wrote a brief manual on the structure of the language, and here are two versions of it: an early, very-nearly-complete one and a later, not-quite-so-complete one (pages 4 & 7 are missing). The last page in the gallery is a List of Grammatical Words and Symbols.