Ramanandi sect believes that Rama has a planet in Vaikuntha called Sakethloka. Are there any scriptural references for this loka?
Yes, there are references of Saketa AKA Ayodhya in scriptures:
The Shiva Samhita mentions there are two Ayodhyas- Para-Ayodhya which exists outside the material universe and the Ayodhya on Earth where Sri Rama descended:
The Para-Ayodhya is where Bhagavan disports while Ayodhya on the Earth is where Bhagavan indulges in divine play. Bhagavan Sri Rama is the Supreme Lord of both these Lokas. Whatever is present in Para-Ayodhya is also present in the Ayodhya on the Earth. (Shiva Samhita, Canto V, Chapter II)
The Vashishtha Samhita states that Saketa-Loka encompasses all the Lokas situated outside the material universe:
Saketa-Loka is itself a form of Truth, Consciousness, Supreme Bliss. All the abodes of Vishnu and Goloka are a part of the eternal Saketa-Loka. (Vashistha Samhita)
Lastly, in the Padma Purana, it is described that Ayodhya lies on the centre of Vaikuntha:
Beyond these Lokas lie the Supreme abode of Vishnu. The devotees and servants of the Lord resides in this Supreme abode of Bhagavan Vishnu, the very embodiment and bestower of Supreme Bliss. At the very centre of this Loka, is situated, the divine city by the name of "Ayodhya", which is adorned and filled all around by beautiful and magnificent structures. (Padma Purana 6.228.10-12)