Is any scripture says Kabandha, a demon who appears in Ramayan, having no head or neck with one large eye on the breast and a mouth on the stomach?
The form of Kabandha is described in Valmiki Ramayana, Aranya Kanda, Chapter 69. But it is not exactly same as the wikipedia link you have mentioned.
आसेदतुः च तत् रक्षः तौ उभौ प्रमुखे स्थितम् |
विवृद्धम् अ-शिरो ग्रीवम् कबंधम् उदरे मुखम् || ३-६९-२७
Then they both had to drew nigh of a waylaying demon Kabandha, who is situated frontally with an overgrown body, which is neckless, ergo headless, ergo mouth in paunch. [3-69-27]
रोमभिर्निश्चितैस्तीक्ष्णैर्महागिरिमिवोच्छ्रितम् - यद्वा -
रोमभिः निचितैः तीक्ष्णैः महागिरिम् इव उच्छ्रितम् |
नील मेघ निभम् रौद्रम् मेघ स्तनित निःस्वनम् || ३-६९-२८
That diabolical demon is peaking like a huge mountain, his hair is horripilate and thickset, and his gleam is like a dark cloud, and his sounding is like a thunder. [3-69-28]
अग्नि ज्वाल निकाशेन ललाटस्थेन दीप्यता |
महापक्षेण पिंगेन विपुलेन आयतेन च || ३-६९-२९
एकेन उरसि घोरेण नयनेन आशु दर्शिना |
महा दंष्ट्र उपपन्नम् तम् लेलिहानम् महा मुखम् || ३-६९-३०
Only one ochry eye blazing like the tongue of an inferno is there on his forehead, which forehead situated on his chest. That single eye with incisive and sharp-sight is broad beaming and wide angling, on which there are winglike eyelids. That monster is now licking his giant mouth that is stuffed with spearhead like fangs, as he has just finished a gobble, and the brothers had to drew nigh of such a demon. [3-69-29, 30]
भक्षयंतम् महा घोरान् ऋक्ष सिम्ह मृग द्विपान् |
घोरौ भुजौ विकुर्वाणम् उभौ योजनम् आयतौ || ३-६९-३१
He is eating the highly brutal bears, lions, predators, and elephants, and he is outstretching both of his deadly arms, each of which is stretchable to a yojana distance, and the bothers neared such a demon. [3-69-31]
Why does he have only one eye instead of normally two eyes and with an odd figure?
Kabandha was originally a son of Danu and had a beautiful body. He pleased lord Brahma with penance and get the boon of long life. But due to pride of that boon he battled with lord Indra. But Indra used his Vajra weapon to drove his head and thighs into his body. So his form changed. It is described in Valmiki Ramayana, Aranya Kanda, Chapter 71.
श्रिया विराजितम् पुत्रम् दनोः त्वम् विद्धि लक्ष्मण || ३-७१-७
इन्द्र कोपात् इदम् रूपम् प्राप्तम् एवम् रण आजिरे |
"Oh, Lakshmana, you may know as the most handsome son of Danu, and this misshapen form has chanced on me owing the ire of Indra in battlefield... [3-71-7b, 8a]
अहम् हि तपसा उग्रेण पितामहम् अतोषयम् || ३-७१-८
दीर्घम् आयुः स मे प्रादात् ततो माम् विभ्रमो अस्पृशत् |
"I have gladdened Grandparent Braham with severe ascesis and He granted longevity to me, and then a kind of recalcitrance touched off in my mind... [3-71-8b, 9a]
दीर्घम् आयुः मया प्राप्तम् किम् मे शक्रः करिष्यति || ३-७१-९
इति एवम् बुद्धिम् आस्थाय रणे शक्रम् अधर्षयम् |
" 'When longevity is acquired by me what Indra can do to me...' thus relying upon that kind of certitude, I jousted with Indra in a bout... [3-71-9b, 10a]
तस्य बाहु प्रमुक्तेन वज्रेण शत पर्वणा || ३-७१-१०
सक्थिनी च शिरः चैव शरीरे संप्रवेशितम् |
"But the Thunderbolt that has a hundred cutting edges and that which is launched from Indra's hand has rammed by head and thighs into my body... [3-71-10b, 11a]
स मया याच्यमानः सन् न आनयत् यम सादनम् || ३-७१-११
पितामह वचः सत्यम् तत् अस्ति इति मम अब्रवीत् |
"When I begged of him saying, 'lead me to the hell of Yama, rather than making me to live this hell of a body...' Then Indra said this to me, 'Let the Grandparent Brahma's word about your longevity come true...' Thus Indra spared me to me... [3-71-11b, 12a]
अनाहारः कथम् शक्तो भग्न सक्थि शिरो मुखः || ३-७१-१२
वज्रेण अभिहतः कालम् सु दीर्घम् अपि जीवितुम् |
" 'By the impaction of Thunderbolt disarranged are my thighs and head, thereby my mouth went into my stomach... and without thighs how can I prowl, without arms how can I scrabble, and without a mouth how can I guzzle... and how am I capable to live on, and even that living too, is destined for too long a time...' [3-71-12b, 13a]
स एवम् उक्तः मे शक्रो बाहू योजनम् आयतौ || ३-७१-१३
तदा च आस्यम् च मे कुक्षौ तीक्ष्ण दंष्ट्रम् अकल्पयत् |
"When I said to Indra this way, Indra devised for me yojana long arms, also that way a rapier-fanged mouth in my paunch... [3-71-13b, 14a]